Jeremy Corbyn's referendum pledge is a fragile fix for a splintering Labour party

The wheels quickly started wobbling off Corbyn's Final Say soap cart

So are we poised to hold a new referendum? The jubilation in the camp of those campaigning to reverse Brexit should be put on hold until we see evidence that there is firstly a broad-based, united campaign by the Labour leadership and secondly, that most Labour MPs make a new vote the centrepiece of their approach to Brexit.

In the absence of those things, we move quickly back to the old dreary territory of Labour insisting on the BBC this morning that the Commons should vote for Labour’s version of its cake-and-eat-it Brexit based on a surreal customs union arrangement which would allow a Labour Britain to be in “a”, but not “the” Customs Union with a right to have a say on overall EU trade policy.

That does not exist today and is incompatible with WTO rules. You are either in a customs union or not.

Labour also wants its fantasy “close alignment” with the single market while still being able to pick and chose the bits of the EU single market it does not like. All EU 27 members would prefer that version of the single market but it is not on offer.

If Labour put their unicorn version of Brexit to the Commons it will be rejected. Thereafter Labour says it will call for a new referendum to reject Theresa May’s deeply flawed deal. Her deal means the UK leaves the EU Treaty on 29 March but stays in the EU in economic and trade terms, including freedom of movement, while Brussels and London negotiate the terms of a future relationship based on the framework set out over the 147 paragraphs of the political declaration.

These are full of contradictory assertions. They do not cover the service sector – 80 per cent of the UK economy – and by the standards of most EU agreements with third countries (which is what the UK will become) will take 5-10 years to complete. In that period there will be no certainty for business, above all foreign investors like Japanese car-makers or Airbus.

Labour quite rightly says this deal is very bad for Britain. Yet those arguing for the people to be given a chance to cast their verdict on this future disaster have been treated with indifference bordering on hostility by endless shadow cabinet ministers in the last 18 months.

Pro-European Labour MPs like Lucy Powell or Stephen Kinnock or Labour grandees like Lord Charlie Falconer have all opposed a Final Say. They have joined the more predictable anti-European, rent-a-quote Labour MPs who get more headlines than their colleagues with strident opposition for the right of the people to be consulted.

Up to a few days ago this line against a new referendum seemed to find favour in the inner circles of the Labour leadership. The trade union leader closest to Corbyn is Unite’s general secretary, Len McLuskey. He has never made a secret of his contemptuous hostility towards the idea.

So what has happened to produce this U-turn in favour of a referendum? Step forward the nine Labour MPs who resigned from the Labour Party to form The Independent Group (TIG). There is a 10th, Ian Austin, who is anti-Corbyn as a future prime minister but who supports Brexit and May’s Deal.

The shockwaves in Labour as every MP looked at friends and colleagues and asked “who’s next?” should not be underestimated. Equally significant was an opinion poll this week which showed Labour’s vote slumping to just 23 per cent. Another poll showed that 84 per cent of voters who had reached voting age since 2016 wanted to stay in Europe and 87 per cent said they would oppose May’s deal in a referendum.

It was simply no longer tenable to stay in the same trench of relegating a fresh vote to some far-off horizon – the trench in which Corbyn and his shadow ministers have been crouching since Labour activists voted for a new referendum at the party conference last September.

So Corbyn moved up and out into the open with yesterday’s announcement to the weekly meeting of Labour MPs in the Commons. It won the desired headlines and left the defecting MPs munching their Nando’s chicken looking rather lonely as their main reason for leaving Labour – Corbyn’s refusal to support a new vote – had now disappeared.

But the wheels quickly started wobbling off the new Corbyn referendum soap cart. When his foreign affairs spokesperson, Emily Thornberry, said Labour would campaign to stay in the EU in a referendum, a senior Corbyn aide, said Labour would not. A significant number of Labour MPs said they would oppose the call for a new public vote.

Unless, it has the support for a good number of Tory MPs, Labour’s new referendum proposal will fail to win support in the Commons. This will allow Corbyn to wash his hands of responsibility by saying: “I tried to win support for a new referendum but the Commons rejected it.”

Let us see if all of Labour’s shadow cabinet, as they fan out to do media interviews and address party meetings, show enthusiasm and energy in denouncing Brexit, and the flawed corrupted plebiscite of lies of June 2016.

Corbyn’s announcement is a potential game-changer but only if he and Labour play a new game of support for Britain in Europe – something Corbyn has opposed since he joined the Labour party half a century ago.