Boris Johnson will be embarking on “a kamikaze act” that will force him out of No 10 if he tries to deliver Brexit without a fresh referendum, a new cross-party study of his options warns.

All other possible routes out of the crisis – demanding a fresh deal from the EU, tweaking Theresa May’s failed deal, pursuing a no-deal Brexit, or a general election – are doomed to fail, it concludes.

The man poised to become prime minister next week would then be forced to suspend parliament, to force through a no-deal – but would be toppled immediately afterwards even if he succeeded, it argues.

“If a new prime minister prorogued parliament to force it through, it is inconceivable that they would retain the confidence of the House of Commons, so it would be a kamikaze act,” says the study endorsed by Tory rebel Dominic Grieve.

Crucially, Mr Johnson is also warned that his expected sacking of pro-EU cabinet heavyweights could finally deliver a Commons majority for a Final Say referendum.

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The chancellor Philip Hammond, David Gauke, the justice secretary, Rory Stewart, the international development secretary, and Greg Clark, the business secretary, are likely to be “free” to oppose Mr Johnson.

“Pragmatic Conservative MPs will have to vote for something. None have advocated a general election, which could be disastrous for their party,” says the report, for the People’s Vote campaign.

“Many know that no deal would be a catastrophic outcome. So, the attractiveness of a People’s Vote as the only viable route will grow.”

The study, entitled Six Dead Ends, One Cliff-Edge, Only One Way Out, sets out to show how that Mr Johnson will fail if he attempts to solve the Brexit impasse by:

* Changing, or stripping out, the Irish 'backstop' from the divorce deal – because the idea “was tested to destruction by Theresa May” and the EU’s view “has not changed”.

* A Northern Ireland-only backstop – because the risk to the peace process would risk the collapse of the government.

* “Tweaking” the withdrawal agreement – with “cosmetic changes to the backstop or a longer transition period” – which would also fail to secure a majority.

* An autumn general election – with the Tories floundering in the polls, Mr Johnson would be at risk of beating George Canning’s 1827 record as the shortest-serving prime minister in history.

* Pursuing a no-deal Brexit – arguing MPs will be able to use a “series of procedural devices” to block a crash-out departure.

In contrast, the report argues, the EU would agree an Article 50 extension for a new referendum next Spring, allowing “a resolution of the Brexit crisis”.

Mr Grieve, a former attorney general, said: “Some of us see such a referendum as our best hope of stopping Brexit. But more and more Conservatives see it as a way of breaking the deadlock and delivering Brexit.

“Either way, it is a democratic answer to a question that threatens not only our party but also our country.”

And Margaret Beckett, a former Labour foreign secretary, said: “As the UK stumbles towards the new Brexit deadline of 31 October, these undeliverable, unattractive or unedifying proposals are making the UK’s position look ever more precarious.

“There is only one viable solution and it is also happens to be the most democratic. A People’s Vote is the only way out of this crisis.”