Most Tory voters think the party would be better off with Boris as leader, new poll reveals - while few believe Theresa May will fight the next election 

• Tory voters do not believe Theresa May will fulfil her vow to stay on in No 10
• Conservative supporters feel best hope of election win would be with new leader
• It is first survey carried out after PM's surprise 'I'm not quitting' declaration

Tory voters do not believe Theresa May will be able to fulfil her vow to stay on in No 10 and fight the next Election – and feel their best hope of winning would be under a new leader.

Nor do the public believe she has the guts to go through with her threat to walk away with no deal if the increasingly fractious Brexit negotiations collapse.

They are among the main findings of a new poll from Survation – the only opinion pollsters to predict the last General Election correctly – for The Mail on Sunday.

It is the first survey carried out after the Prime Minister's surprise 'I'm not quitting' declaration during her trade trip to Japan last week.

In addition to showing Labour with a five-point lead over the Conservatives, our poll shows voters believe that, if Mrs May and Jeremy Corbyn both lead their respective parties into the Election due by 2022, Corbyn will win, albeit by a tiny margin.

But there is no such uncertainty as to who the Conservatives should turn to if they wish to revive their electoral fortunes: Boris Johnson.

In a timely boost, the Foreign Secretary, dismissed as an 'international joke' by the Times newspaper last week, is the clear favourite heir to May among the public as a whole, and significantly, among people who voted Conservative at the last Election.

More surprisingly, his nearest leadership rival is maverick Old Etonian and 'hard Brexiteer' Jacob Rees-Mogg, dubbed 'the new Boris' by some. As a mark of how seriously Tory voters take the increasingly ambitious Rees-Mogg, in a run-off between Jacob and Boris, Johnson wins by only two percentage points, according to the poll.

Chancellor Philip Hammond is third favourite to succeed May, followed by Brexit Secretary David Davis and Home Secretary Amber Rudd.

About four in ten Tory voters say it is unthinkable that May will lead the Tories at the next Election; one in three believe it is possible.

A total of 27 per cent of Conservatives say replacing her would give them a better chance of winning the next Election; 19 per cent say it would make it less likely.

A total of 11 per cent of Tories want Mrs May to stand down this year; 26 per cent say she should do so after Brexit in 2019; and 54 per cent say she should lead them into the next Election.

The poll also suggests voters are unconvinced by her tough talk on Brexit, specifically her repeated commitment to walk away from the talks if she is not satisfied with the deal offered by Brussels.

Nearly half of those surveyed say she is 'bluffing', against fewer than one in five who believe her. The scepticism is shared by Tory supporters: 35 per cent say she is 'bluffing' compared to 14 per cent who say will go through with it.

Almost six out of ten voters say it would be 'bad' for the UK to leave the EU without a Brexit deal. Corbyn's decision to back staying in the single market and customs union in a transitional period after Britain leaves the EU is supported by 42 per cent of voters, with 28 per cent against. Asked if the Prime Minister should follow suit, 37 per cent of Conservatives urge her to do so against 46 per cent who say she should not.

Survation interviewed 1,046 people online on Thursday and Friday.