Sign up to our free Brexit and beyond email for the latest headlines on what Brexit is meaning for the UK Sign up to our Brexit email for the latest insight
Implementing Boris Johnson 's Brexit deal by the end of next year will be "major" challenge, a leaked Whitehall memo has warned.
The document, drawn up by the Department for Exiting the European Union , raises questions about the prime minister's promise that the UK will be able to fully leave the EU at the end of 2020.
It warns that introducing new infrastructure in Northern Ireland within 12 months will be difficult and says there would be a "legal and political impact" of failing to do so.
The document, marked "Official Sensitive" but seen by the Financial Times , was sent to senior Whitehall officials last week.
It said: “Delivery of the required infrastructure, associated systems, and staffing to implement the requirements of the protocol by December 2020 represents a major strategic, political and operational challenge.”
It admits that there would be a “legal and political (domestic and EU) impact of not being able to deliver the protocol in December 2020”.
The memo also warns that “delivery on the ground would need to commence before we know the outcome of negotiations” on the free trade deal with the EU that Mr Johnson has insisted he will be able to agree next year.
The prime minister has repeatedly insisted that his deal will allow the UK to fully leave the EU by the end of 2020.
He has also claimed that it will not lead to checks on goods travelling between Northern Ireland and the rest of the UK, despite leaked government documents and the Brexit secretary, Steve Barclay, having said otherwise.
On Monday, Arlene Foster , leader of the Democratic Unionist Party (DUP), said HM Revenue & Customs experts had confirmed to her that there would need to be checks on goods.
She told BBC Radio 4's Today : “You can’t leave part of the UK in a worse off position and have checks between different parts of the UK.”
Show all 114 1 /114General election: On the campaign trail General election: On the campaign trail Boris Johnson drives a Union flag-themed JCB, with the words "Get Brexit Done" inside the digger bucket, through a fake wall emblazoned with the word "GRIDLOCK", during a general election campaign event at JCB construction company in Uttoxeter, Staffordshire
AFP via Getty
General election: On the campaign trail A sculpture of an owl is bedecked with an EU beret as Liberal Democrat leader Jo Swinson gestures during an interview at a general election campaign event in Bath
AFP via Getty
General election: On the campaign trail Boris Johnson (C) talks during a question and answer session on a general election campaign visit to Ferguson's Transport in the town of Washington, west of Sunderland
AFP/Getty
General election: On the campaign trail Boris Johnson tries to save a shot during a warm up before a girls football match while on the campaign trail in Cheadle Hulme, northwest England
POOL/AFP via Getty
General election: On the campaign trail Jeremy Corbyn makes cup of coffee as he campaigns in Barry, south Wales
AFP
General election: On the campaign trail Nicola Sturgeon poses as she launches the SNP campaign bus tour, at Queensferry Crossing in Edinburgh, Scotland
AFP via Getty
General election: On the campaign trail Boris Johnson reacts as he changes a wheel of a Formula One car during a Conservative Party general election campaign visit to Red Bull Racing in Milton Keynes
POOL/AFP via Getty
General election: On the campaign trail Britain's Prime Minister Boris Johnson visits a Christmas market in Salisbury
REUTERS
General election: On the campaign trail Liberal Democrat Leader Jo Swinson on the election campaign bus on route to Chelmsford
PA
General election: On the campaign trail Labour leader Jeremy Corbyn talking to a university worker outside Birkbeck/SOAS University of London, at the announcement of his parties of the plan for the extension of workers' rights
PA
General election: On the campaign trail Nicola Sturgeon plays a game with string during a visit to Perth and District YMCA
Getty Images
General election: On the campaign trail Brexit Party leader Nigel Farage picks up a copy of The Brexiteer during a visit to JPI Printers in Dinnington
PA
General election: On the campaign trail Boris Johnson, centre, talks to veteran James Gammer as he visits a veterans centre
AP
General election: On the campaign trail SNP supporters meet First Minister Nicola Sturgeon following her address during a St Andrews day election speech
Getty
General election: On the campaign trail Jeremy Corbyn has a photo taken outside Birkbeck/SOAS University
PA
General election: On the campaign trail Liberal Democrat leader Jo Swinson during a visit to the Cardiff United Synagogue
PA
General election: On the campaign trail Brexit Party leader Nigel Farage reacts as he attends an election debate
ITV/Reuters
General election: On the campaign trail Jeremy Corbyn wears a jacked displaying Labour's slogan 'For the many, not the few'
EPA
General election: On the campaign trail Prime Minister Boris Johnson on The Andrew Marr Show
Getty
General election: On the campaign trail Nicola Sturgeon plays with local children during a visit to the Jelly Tots & Cookies Play Cafe in Uddingston, South Lanarkshire
PA
General election: On the campaign trail Opposition Labour Party leader Jeremy Corbyn eats some chips in Whitby, northern England
AFP via Getty
General election: On the campaign trail Boris Johnson and Conservative MP George Eustice, left, tour 'Rodda's Clotted Cream' whilst campaigning in Cornwall
Getty
General election: On the campaign trail Jo Swinson during a visit to Dunkertons Cider Company, an organic and plastic free brewery in Cheltenham
PA
General election: On the campaign trail Jeremy Corbyn holds up unreacted documents with NHS staff. Mr Corbyn released uncensored official documents which he says provides confirmation that the NHS is on the table in trade talks with the USA
EPA
General election: On the campaign trail Nigel Farage meets locals in Barnsley market
PA
General election: On the campaign trail Nicola Sturgeon launches the SNP's general election manifesto
Getty
General election: On the campaign trail Labour Party leader Jeremy Corbyn addresses the audience during the launch of Labour's environmental policy in Southampton
Getty
General election: On the campaign trail Boris Johnson tries an apple as he visits Healey's Cornish Cyder Farm in Callestick
AP
General election: On the campaign trail Jo Swinson helps make a chicken tikka masala during a visit to the Ashoka restaurant in Bearsden, Glasgow
PA
General election: On the campaign trail Nigel Farage playing golf on a range at One Stop Golf in Hull
PA
General election: On the campaign trail Jeremy Corbyn addresses the audience during a climate emergency rally in Falmouth
Getty
General election: On the campaign trail Liberal Democrat leader Jo Swinson meets supporters during a visit to Dunkertons Cider Company
PA
General election: On the campaign trail Boris Johnson visits Chulmleigh College
AP
General election: On the campaign trail Labour Party leader Jeremy Corbyn as he appearing on the BBC political programme The Andrew Neil Show. The opposition leader defended his handling of anti-Semitism allegations after Britain's most senior rabbi suggested the issue was a "new poison" within the party that had been "sanctioned from the very top". In an unprecedented intervention ahead of next month's election, Chief Rabbi Ephraim Mirvis suggested Corbyn was "unfit for high office" due to his perceived failure to clamp down on the problem within the party
BBC/AFP via Getty
General election: On the campaign trail
PA
General election: On the campaign trail Prime Minister Boris Johnson launches the Conservative Party Scottish Manifesto in North Queensferry
Getty
General election: On the campaign trail Britain's Opposition leader Jeremy Corbyn poses with WASPI (Women Against State Pension Inequality) supporters after he outlined Labour's plans to repay the "historical debt of honour" owed to women born in the 1950's
AFP via Getty
General election: On the campaign trail Jo Swinson alongside the Lib Dem's candidate for Truro and Falmouth, Ruth Gripper, and founder of Finisterre, Tom Kay, during a tour of the British surfing brand, which creates sustainable surfing gear, in St Agnes, Cornwall
PA
General election: On the campaign trail Prime Minister Boris Johnson poses with sheep as he visits the Royal Welsh Showground, in Llanelwedd
PA
General election: On the campaign trail A coalition of NHS (National Health Service) campaigners led by "Keep Our NHS Public" and "We Own It", pose for photographs with masks of US President Donal Trump, right, and Prime Minister Boris Johnson carving up the NHS with a giant knife and fork, as they take part in a demonstration on Parliament Square. The campaigners are calling for the NHS to be taken "off the table" in a trade deal with the US by ending privatisation in the health service and restoring it to a wholly publicly owned and provided service
AP
General election: On the campaign trail Brexit Party leader Nigel Farage visits Plymouth Fisheries at Sutton Harbour
Getty
General election: On the campaign trail SNP leader Nicola Sturgeon gives her party's candidate for North East Fife Stephen Gethins a haircut, during a visit to Craig Boyd Hairdressing in Leven
PA
General election: On the campaign trail Vans belonging to The Community United against Labour Party anti-Semitism group, Culpa, parked next to a police car ahead of the Labour Race and Faith Manifesto launch
Getty
General election: On the campaign trail Boris Johnson prepares to serve food at the Royal Welsh Showground
PA
General election: On the campaign trail Jeremy Corbyn tries his hand at bricklaying during a visit to the West Nottinghamshire College Construction Centre, in Ashfield
PA
General election: On the campaign trail Liberal Democrat leader Jo Swinson during a visit to the London design museum to discuss the party's tech policy
PA
General election: On the campaign trail Brexit Party leader Nigel Farage visits Seaham
Getty
General election: On the campaign trail Britain's Prime Minister Boris Johnson arrives for the Conservative party's manifesto launch in Telford
Reuters
General election: On the campaign trail Labour Party leader Jeremy Corbyn meets supporters during a visit to Thurrock in Essex
PA
General election: On the campaign trail Protesters wait for the arrival of Prime Minister Boris Johnson ahead of the launch of his party's manifesto
PA
General election: On the campaign trail Jo Swinson gestures from atop a crane during a visit to an eco home building site in Sheffield
AFP via Getty
General election: On the campaign trail Jeremy Corbyn meets a supporter on a train on his return from a visit to Sheffield
PA
General election: On the campaign trail Prime Minister Boris Johnson during a visit to Bassetlaw District General Hospital in Worksop, Nottinghamshire
PA
General election: On the campaign trail Nigel Farage campaigns in Hartlepool
Getty Images
General election: On the campaign trail Jeremy Corbyn outside an Amazon depot in Sheffield, to announce plans for a workers' rights revolution and to ensure big businesses pay their fair share of taxes
PA
General election: On the campaign trail Prime Minister Boris Johnson, Liberal Democrat leader Jo Swinson, First Minister of Scotland Nicola Sturgeon and Labour leader Jeremy Corbyn, during their successive appearances on BBC Question Time Leaders' Special at the Octagon in Sheffield
PA
General election: On the campaign trail Liberal Democratic Party leader Jo Swinson visits a primary school in Cambridge
EPA
General election: On the campaign trail Boris Johnson lays a brick during a visit to the Barratt Homes
Getty
General election: On the campaign trail Labour leader Jeremy Corbyn attends the launch of the party's election manifesto at Birmingham City University
Getty
General election: On the campaign trail Brexit Party leader Nigel Farage holds his party policy document during the party's policy launch in Westminster
PA
General election: On the campaign trail SNP leader Nicola Sturgeon joined Dundee East candidate Stewart Hosie to made a keynote speech at The Quay
Getty
General election: On the campaign trail Prime Minister Boris Johnson holds a part of an electrical appliance during a General Election campaign trail stop at Ebac in Newton Aycliffe
AP
General election: On the campaign trail Jeremy Corbyn poses during a visit to The Oatcake Boat on the Trent & Mersey Canal, Stoke
Getty
General election: On the campaign trail Jo Swinson and Willie Rennie Leader of the Scottish Liberal Democrats gesture, during a visit to Glasgow
Reuters
General election: On the campaign trail
PA
General election: On the campaign trail Liberal Democrat leader Jo Swinson (left) during a visit to the Gurdwara Singh Sabha Temple in Glasgow
PA
General election: On the campaign trail Labour leader Jeremy Corbyn meets Colin and his mother after a speech at the University of Lancaster
Getty Images
General election: On the campaign trail Britain's Green Party co-leaders Jonathan Bartley, Sian Berry, and deputy leader Amelia Womack, wave during the launch of the party manifesto at the Observatory at London Wetland Centre
Reuters
General election: On the campaign trail Scottish Nationalist Party leader Nicola Sturgeon meets voters and activists at Cafe Roma in Clarkston, Glasgow
AFP via Getty
General election: On the campaign trail Protestors participate in an anti-Boris Johnson rally in his constituency Uxbridge, west London
AFP via Getty Images
General election: On the campaign trail Brexit Party leader Nigel Farage looks out from a window on the Kestrel crabbing boat in Grimsby fish dock
PA
General election: On the campaign trail Prime Minister Boris Johnson on a tug boat in the port of Bristol
PA
General election: On the campaign trail Green Party Co-Leader Sian Berry has a selfie taken with a supporter at the Observatory, London Wetlands Centre
PA
General election: On the campaign trail Jo Swinson helps chef Leonardo Mastofilippo to make pizza during a campaign visit to cafe Amisha in South Bermonsey
EPA
General election: On the campaign trail Labour leader Jeremy Corbyn with WASPI (Women Against State Pension Inequality) ladies during a visit to Birkenshaw Sports Barn in Uddingston
EPA
General election: On the campaign trail Boris Johnson at the unveiling of the Conservative Party battlebus in Middleton, Greater Manchester
PA
General election: On the campaign trail Nicola Sturgeon sits alongside Cycling Without Age user Cyril Corcoran (centre), aged 78, in an electric tricycle during a visit to Hawick, in the Scottish Borders
PA
General election: On the campaign trail Nigel Farage holds a fish during a stop at the Grimsby Seafood Village
PA
General election: On the campaign trail Liberal Democrats leader Jo Swinson in the boxing ring at Total Boxer, a specialised boxing gym which offers training to young people as a means of keeping them away from violence, in Crouch End, London
PA
General election: On the campaign trail Britain's Prime Minister Boris Johnson reacts as he participates in a school art lesson, making a clay figure at George Spencer Academy, west of Nottingham
AFP via Getty
General election: On the campaign trail Labour Party leader Jeremy Corbyn during a visit to the Heart of Scotstoun Community Centre in Glasgow
PA
General election: On the campaign trail Scotland's First Minister and SNP leader Nicola Sturgeon visits the Cafe Gelato in Rutherglen, Glasgow
EPA
General election: On the campaign trail The Green Party launch in Bristol
PA
General election: On the campaign trail Farage enjoys some chips at the start of a nationwide tour for the 2019 general election, in Whitehaven
AFP/Getty
General election: On the campaign trail Labour leader Jeremy Corbyn unveils the Labour battle bus in Liverpool
PA
General election: On the campaign trail Boris Johnson reacts as he talks with workers whilst weighing packaged tea bags at the Tetley Tea Factory in Stockton-on-Tees
AFP/Getty
General election: On the campaign trail Brexit Party leader Nigel Farage on the campaign trail in Whitehaven, where he was confronted by Karl Connor
PA
General election: On the campaign trail Lib Dem leader Jo Swinson speaks to volunteer Rosie Squires in the Stainforth 4 All charity shop during a visit to Stainforth in South Yorkshire to meet people affected by flooding
PA
General election: On the campaign trail Nicola Sturgeon poses with candidates during the SNP general election campaign launch in Edinburgh
Reuters
General election: On the campaign trail Labour Party leader Jeremy Corbyn with Laura McAlpine, the party's candidate for Harlow
PA
General election: On the campaign trail Anti-Boris Johnson protesters demonstrate outside the hall where the Conservative Party were launching their campaign in Birmingham
EPA
General election: On the campaign trail Green Party Co-Leader Sian Berry (left), Deputy Leader and Parliamentary Candidate for Newport West Amelia Womack (right), and Bristol West Candidate Carla Denyer (centre) at the launch of the party's general election manifesto in Bristol
PA
General election: On the campaign trail The PM tastes whisky during a visit to Diageo's Roseisle Distillery near Elgin, Scotland
Reuters
General election: On the campaign trail Nigel Farage poses with boxer Dereck Chisora during a visit to a boxing gym in Ilford
Reuters
General election: On the campaign trail Jo Swinson visits a science class at Hinchley Wood School near Esher
Reuters
General election: On the campaign trail First Minister Nicola Sturgeon holds a guitar as she visits Dalkeith Community Hub
Getty
General election: On the campaign trail A man heckles as Jeremy Corbyn gives a speech at the Senior Citizens Hall in Macclesfield
Getty
General election: On the campaign trail Britain's opposition Labour Party leader Jeremy Corbyn visits residents affected by flooding in Conisbrough
Reuters
General election: On the campaign trail Boris Johnson gestures as he helps quality control staff during a visit to the Tayto Castle crisp factory in County Armagh, Northern Ireland
AFP via Getty
General election: On the campaign trail The Lib Dem leader eats a marshmallow during a visit to Free Rangers Nursery in Midsomer Norton, Somerset
PA
General election: On the campaign trail Nigel Farage visits a butcher's shop in Sutton-in-Ashfield
Reuters
General election: On the campaign trail SNP leader Nicola Sturgeon visits Blosson Tree children's nursery
AFP via Getty
General election: On the campaign trail Jeremy Corbyn laughs during a visit to the Scrap Creative Reuse Arts Project, Sunny Bank Mills
Getty
General election: On the campaign trail Prime Minister Boris Johnson hold Rosie the rabbit during a visit to a primary school while on the campaign trail in Taunton
AFP via Getty
General election: On the campaign trail Jo Swinson playing with children at the Battersea Arts Centre in Lavender Hill
PA
General election: On the campaign trail Farage addresses supporters at the Washington Central Hotel in Workington
PA
General election: On the campaign trail Jeremy Corbyn poses with Labour activists as they canvas in Govan, Glasgow
PA
General election: On the campaign trail Nicola Sturgeon during a visit to The Shed, a Climate Challenge community project at North Edinburgh Arts
PA
General election: On the campaign trail Prime Minister Boris Johnson meets six month old Willow Rose Anderson, at the Lych Gate Tavern in Wolverhampton
PA
General election: On the campaign trail Jo Swinson holds up a sack of barley during a visit to Crafty Maltsters Scotland
Getty
General election: On the campaign trail Jeremy Corbyn tries a scone in Bentley, Doncaster
PA
General election: On the campaign trail Nigel Farage takes a mouthful of homemade cheesecake during a stop at the Grimsby Seafood Village
PA
General election: On the campaign trail Boris Johnson hauling a consignment of frozen chocolate gateaux, during a visit to Iceland Foods HQ in Deeside
PA
General election: On the campaign trail Jo Swinson puts on a high visibility jacket during a visit to Sigma Pharmaceuticals, a family run pharmaceutical wholesaler in Watford
AFP via Getty
Asked about the leaked document, Rishi Sunak, the chief secretary to the Treasury, insisted that the deal could be implemented within a year.
He told Today : "People said it would be impossible for the prime minister to get a new deal - many people came on your show and said exactly that. He's shown his ability to actually negotiate well and get things done for this country.
"Coming from a business background myself, having a deadline concentrates minds and we've agreed this timeframe with the European Union and we do think it's deliverable."
He added: "Having sat on a committee, chaired by Michael Gove, to plan for our departure from the European Union, I've actually been incredibly impressed by all the preparations that have gone on that mean that we are in very good shape not just to deal with new trading relationships but all the other things."
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies