The Labour leader has abandoned a plan to head a minority government to implement his manifesto if Boris Johnson is toppled in a no-confidence vote, and promised to call an immediate general election instead.
The move is designed to break the parliamentary deadlock that threatens to wreck attempts to stop the UK crashing out of the EU on 31 October.
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He has also dangled a promise of a Final Say referendum on Brexit, if Labour wins the general election after his “strictly time-limited” caretaker government.
Mr Corbyn hopes to convince the Liberal Democrats, the Scottish Nationalist Party and rebel Tories that he can be trusted to be the leader sent to Brussels to delay Brexit by agreeing an Article 50 extension. However, the Lib Dems have already rejected this offer, claiming he is not the man to build a majority against a no-deal Brexit in the Commons.
In a letter, Mr Corbyn repeats his intention to “table a vote of no confidence at the earliest opportunity when we can be confident of success”, after MPs return next month.
He then writes: “I would then, as leader of the opposition, seek the confidence of the House for a strictly time-limited temporary government with the aim of calling a general election, and securing the necessary extension of Article 50 to do so.
“In that general election, Labour will be committed to a public vote on the terms of leaving the European Union, including an option to Remain.
“I would welcome the chance to discuss these proposals further with you, which I hope can halt the serious threat of no deal, end the uncertainty and disarray, and allow the public to decide the best way ahead for our country.”
Responding to the letter, Ms Swinson said: “Jeremy Corbyn is not the person who is going to be able to build an even temporary majority in the House of Commons for this task – I would expect there are people in his own party and indeed the necessary Conservative backbenchers who would be unwilling to support him. It is a nonsense.
“This letter is just more red lines that are about him and his position and is not a serious attempt to find the right solution and build a consensus to stop a no-deal Brexit.
“I am committed to working in a credible way with those in other parties, and none, across parliament to stop a no-deal Brexit.”
Attempts to win cross-party agreement on a so-called government of national unity – to be formed if Mr Johnson is defeated – have floundered over who would lead it.
Last week, John McDonnell, the shadow chancellor, vowed to “send Jeremy Corbyn in a cab to Buckingham Palace to say ‘we’re taking over’ to the Queen”.
He rejected any alternative, more neutral caretaker leader, saying: “I think we’d form a minority government, seek to implement our manifesto and we’d expect the other opposition parties and other MPs to vote for those policies.”
However, it is unclear whether Mr Corbyn’s new offer will be sufficient to achieve a breakthrough – given the fierce opposition to putting him in No 10 at all.
Potential rebel Tories have warned they were being driven away from supporting a no-confidence vote by Mr Corbyn’s insistence he must be prime minister, one putting the chances of forming an alternative government at “nil”.
And Chuka Umunna, the Labour defector to the Liberal Democrats, said he must be “open to other suggestions”, with even “a substantial minority of Labour MPs” opposed.
Under the Fixed-term Parliaments Act, MPs have 14 days in which to form a new government, if the sitting premier loses a confidence motion, before an election is held.
But, crucially, Dominic Cummings, the prime minister’s controversial senior aide, has privately threatened there would be no election until after 31 October – ensuring a no-deal Brexit is carried out first.
Mr Corbyn has also received a reply from the UK’s most senior civil servant, after demanding he intervene to prevent such a crash-out Brexit during an election campaign.
The Labour leader wrote to Sir Mark Sedwill, the cabinet secretary, to accuse the prime minister of plotting an “unprecedented, unconstitutional and anti-democratic abuse of power”, because major policy decisions are barred during campaigning.
Mr Corbyn declined to release the reply, but protested it had been “non-committal”.
The Independent understands that, on the question of rules, Sir Mark promised “full and proper application according to circumstances at the time” – without setting out his interpretation of those rules.