EU Referendum: Tony Blair and John Major warn Brexit could lead to break-up of UK

Both men played crucial roles in the Northern Ireland peace process

Sir John Major and Tony Blair make a joint EU appeal in Derry (Getty)

Sir John Major and Tony Blair have warned that a vote to leave the EU would be a "historic mistake" which could break up the UK.

The former adversaries shared a platform at the Ulster University's Magee campus in Londonderry, and warned that Brexit could threaten Northern Ireland's hard-fought peace process.

Sir John said: "I believe it would be an historic mistake to do anything that has any risk of destabilising the complicated and multi-layered constitutional settlement that underpins stability in Northern Ireland."

Both men played crucial roles in the Northern Ireland peace process, and Sir John warned that the wrong outcome on 23 June could "tear apart the UK".

Mr Blair hit out at the Leave campaign, claiming it puts an "ideological fixation" with Brexit ahead of the damage it would cause.

He said: "I say, don't take a punt on these people. Don't let them take risks with Northern Ireland's future. Don't let them undermine our United Kingdom.

"We understand that, although today Northern Ireland is more stable and more prosperous than ever, stability is poised on carefully-constructed foundations.

But the pro-Brexit Democratic Unionist Party deputy leader Nigel Dodds condemned the former prime minister's comments as "irresponsible nonsense".

He said: "Surely this is the most irresponsible talk that can be perpetuated in terms of Northern Ireland – very dangerous, destabilising and it should not be happening," he added during the business statement in the Commons.

Elsewhere, former US president Bill Clinton, whose 1995 visit to Northern Ireland was seen as a crucial moment in the peace process, said he was worried about the potential impact of Brexit on the province.

Writing in the New Statesman magazine, Mr Clinton said: "I was honoured to support the peace process in Northern Ireland. It has benefited from the UK's membership in the European Union, and I worry that the future prosperity and peace of Northern Ireland could be jeopardised if Britain withdraws."

The former president, who worked with Sir John and Mr Blair on the peace process, added: "Transatlantic co-operation is essential, and that co-operation is strongest when Europe is united... I hope you will stay."

Both former prime ministers had integral roles in helping to end the sectarian violence which blighted Northern Ireland for decades.

In 1993, Sir John and Irish prime minister Albert Reynolds delivered the Downing Street Declaration which argued for self-determination on the basis of consent and paved the way for the IRA ceasefires the following year.

Sir John told the audience of teenage schoolchildren who had packed into Magee's Great Hall: "I carried this forward and Tony completed it."

Five years later, in 1998, the British and Irish governments concluded the historic Good Friday Agreement which cemented the stability and laid the foundations for the devolved power-sharing Stormont Executive.

Here are some of the claims made by the two camps:

Remain camp says:

• The border between Northern Ireland and the Republic of Ireland would become the frontier between the EU and a non-EU country if the UK votes to leave. This could mean the return of border control points and customs checks. It could be easier for wanted suspected criminals to dodge justice.
• Britain Stronger In Europe said of the 769 suspects surrendered by other EU countries to the UK under a European Arrest Warrant (EAW) between 2010 and 2015, some 129 – 16% – were handed over by Ireland, second only to Spain. Without access to the EAW, the UK and Ireland would have to negotiate alternative extradition arrangements.
• The peace process ending the Troubles took place within the context of both the UK and Ireland being EU members. The UK-Irish agreement that accompanied the 1998 Good Friday Agreement referred to the two states' wish "to develop still further the unique relationship between their peoples and the close co-operation between their countries as friendly neighbours and as partners in the European Union".
• The EU has a dedicated funding programme to support the peace process, with funds going to both sides of the border. In 2014-2020, the programme is due to receive around £185m.
• Sir John said: "I believe it would be an historic mistake to do anything that has any risk of destabilising the complicated and multi-layered constitutional settlement that underpins stability in Northern Ireland."

Leave camp says:

• The passport-free Common Travel Area has existed since 1923. It is enshrined in UK law and will continue after Brexit. Ireland's ambassador to the UK Daniel Mulhall has insisted the arrangements will "still apply fully".
• Ireland has an opt-out from the Schengen passport-free zone, so migrants will have to pass through either UK or Irish border controls before entering the UK.
• The incentive for migration to the UK via Ireland by EU citizens will substantially diminish after a Leave victory because non-Irish EU migrants will no longer have an automatic right to work.
• The Good Friday Agreement was a bilateral treaty between the governments of Ireland and the UK and did not depend on EU membership and it is "scaremongering" to suggest the peace process could be put at risk.
• Northern Ireland Secretary Theresa Villiers said "whatever the result of the referendum, Northern Ireland is not going back to the Troubles of its past and to suggest otherwise would be highly irresponsible".