Theresa May has privately vowed to thwart any attempt by Boris Johnson to take the UK out of the EU without a deal, her allies have told The Mail on Sunday.

The disclosure comes as senior party figures told The Mail on Sunday that Mrs May had voted for ultra-Remainer Rory Stewart in Thursday's ballot of MPs, which led to a landslide victory for Mr Johnson.

Mrs May, who has vowed to stay on as an MP after she leaves Downing Street next month, has suggested she would join forces with pro-Remain Ministers such as Chancellor Philip Hammond and Pensions Secretary Amber Rudd to try to stop Mr Johnson from leaving after the October 31 deadline 'Deal or No Deal'.

No one ever looked this pleased to see Theresa! Pictured: Former Foreign Secretary Boris Johnson meets association activist to National Conservative Convention Hustings as part of his leadership campaign

Theresa May, pictured today at church, has privately vowed to thwart any attempt by Boris Johnson to take the UK out of the EU without a deal, her allies have said

The scale of Mr Johnson's victory means that, barring a major Boris blow-up, the race has effectively turned into a battle for second place, with his vanquished opponents deciding whether to fight on or clamber aboard his bandwagon.

It is predicted that the Commons contest to whittle down the field of six to a final two will conclude as soon as Wednesday, after two more rounds of votes.

Esther McVey backs Boris for Tory leader Former Tory leadership contender Esther McVey has come out in support of Boris Johnson. Writing in The Sunday Telegraph, Ms McVey - who was eliminated in the first ballot of MPs - said Mr Johnson had agreed to back her agenda for 'blue collar Conservatism'. 'He has promised to deliver Brexit on October 31, deal or no deal, and has shown time and time again that he is a dynamic leader, capable of building a strong team around him that will deliver on his promises,' she wrote. 'Our country is crying out for strong, optimistic leadership and Boris is the man best equipped to take us out of the EU, to transform our country into an outward-looking, confident, self-governing nation, and to implement a policy agenda that will bring back the voters we have lost and ensure we don't allow Jeremy Corbyn's manifesto of economic carnage to plunge us back into the dark ages.' Advertisement

The last two will then face an electorate of more than 160,000 Tory members, after a surge of new members who signed up ahead of the contest were deemed eligible to vote by party chiefs.

Last night Mr Johnson moved to scotch suggestions he wished to avoid a run-off, saying it was 'full steam ahead to a contest'.

Esther McVey, who came last with nine votes on Thursday, was the first former candidate to declare her intentions, saying that she would swing behind Mr Johnson and urging her eight supporters to do the same.

A source said: 'Boris has told Esther that he will give his backing to blue-collar Conservative policies, such as the need to invest in the Midlands and North'.

Health Secretary Matt Hancock, who pulled out on Friday, was last night on the brink of declaring, with friends saying that he was wavering between backing Mr Johnson or Michael Gove – although most expect ambitious Hancock to plump for the frontrunner.

'Matt would be a moderating influence on the likely PM and help unify the party,' the friend said.

In a further boost for Mr Johnson, it is expected that Mrs May's closest Commons aide, Aberdeenshire MP Andrew Bowie, will endorse him to help unify the Scottish party around Mr Johnson's banner.

Mrs May has suggested she would join forces with pro-Remain Ministers such as Chancellor Philip Hammond (left) and Pensions Secretary Amber Rudd (right)

Some of the most intense soul-searching was going on in second-placed Jeremy Hunt's team, with Ms Rudd – who until recently had been poised to form a blockbuster double act with Mr Johnson – angered by Mr Hunt's recent hardline remarks on abortion.

Her views are understood to be shared by Defence Secretary Penny Mordaunt, who has also signed up to Mr Hunt's campaign but warned she would not defend his stance that the legal time limit for a termination should be reduced from 24 weeks to 12.

Yesterday Home Secretary Sajid Javid made an impassioned plea to stay in the race, saying it was not just the 'message that mattered, but the messenger too'.

The size of Mr Johnson's victory has also concentrated minds in the party over his Brexit strategy, and in particular his pledge to leave the EU without a deal if Brussels refuses to make changes to the Withdrawal Agreement.

Where do they stand this morning? What the candidates for Tory leader said as they gear up for the debate Michael Gove Declared himself the 'Chumbawumba candidate' following a decent showing in the first round of voting despite his cocaine revelations, in a reference to a 1997 hit by the anarchist band with the lyrics 'I get knocked down, I get back up again, you're never going to keep me down'. How familiar Tory members will be with the tune waits to be seen. In the Sunday Times he put forth a proposal for a national housing fund paid for by 'Brexit bonds', with home designs to be approved by citizens juries - all of which which has been interpreted as a pitch for the election-battleground portfolio of Communities Secretary in a possible Johnson administration. Mr Gove, who in 2016 said Mr Johnson was not up to the top job, scuppering his former ally's campaign, added: 'I would absolutely work with Boris in any way that he wanted to work with me. No question' Sajid Javid Declaring himself one of only two 'change' candidates in the race, along with Boris, the Home Secretary used an interview in the Sunday Times to point out all his rivals went to Oxford University, while he grew up above his parents' shop and was the first member of his family to go to university. He said he was the leader who could 'look the British public in the eye' as a fellow consumer of state services. In a possible bid to enter the door of Number 11 as Mr Johnson's neighbour, Mr Javid set out his economic credentials, outlining plans for an emergency 'no-deal budget'. Rory Stewart The International Development Secretary told the Sunday Telegraph: 'The other candidates aren't prepared to talk about how they're going to get Brexit done', adding: 'They're just basically saying, Brexit, deliver Brexit. When you say how, answer comes there none. Trust me I'm going to deliver Brexit.' This morning he asked the BBC's Andrew Marr 'How is Boris going to deliver Brexit?' He added: 'I don't even know what he believes. He won't talk to me, he won't talk to you, he won't talk to the public,' as it emerged the front-runner will be empty-chaired at tonight's Channel 4 debate. Dominic Raab Mr Raab, the contest's other remaining hard-Brexiteer, this morning accused rivals of going 'weak at the knees' and defended his decision not to rule out suspending Parliament to push through a no deal Brexit if needs be. He told Sky: 'We gave people a decision. Now Parliament is trying to steal it back away from them. When people voted, they voted to leave.' He added: 'The big mistake we made in these negotiations was taking no-deal off the table. When we start ruling things out we only weaken our chances of getting a deal.' Jeremy Hunt The Foreign Secretary, who came second to Mr Johnson in last week's ballot of Tory MPs, announced an eye-catching policy of offering financial incentives to families who build accommodation for elderly relatives – to help ease the growing social care and childcare burden on the taxpayer. Mr Hunt, who was a distant second in the first round, insisted in the Mail on Sunday he had still not given up hope of winning in the final postal ballot of party members. 'I am the insurgent in this race,' he said. 'I am in it to win it because we have to give the country better choices given the crisis that we're in now.' Today he said he would exhaust all options before contemplating No Deal. 'The difference between me and Boris is I would try for a deal,' he told the BBC's Andrew Marr show. Boris Johnson Mr Johnson remains tight-lipped as his team seeks to avoid doing or saying anything which could undermine their candidate's huge lead among MPs. Mr Johnson was criticised yesterday for busting into a hustings event in London without taking questions from journalists - and sneaking out the back door afterwards. By contrast his rivals stopped to talk to reporters. All six have agreed to take part in the Channel 4 show this evening - but Mr Johnson has made clear he will stay away. Advertisement

Boris Johnson, leadership candidate for Britain's Conservative Prime Minister, leaves home in London, Britain, today

It was Mrs May's failure to secure changes to the deal, and its subsequent rejection by MPs, which led to her downfall. But her allies say she has 'not budged' in her view that the UK should not leave the EU unless a deal has been struck and that to do otherwise would 'jeopardise the integrity of the Union'.

One said: 'She made little secret of the fact that she did not want Boris to succeed her, and if you study everything she has said it is clear where she now is on No Deal. The best hope is that Boris is bluffing as usual.'

Allies of the PM believe that she voted for Mr Stewart in order to 'keep the race interesting' despite claims in Westminster she was backing Jeremy Hunt. The Foreign Secretary's 43 votes match 43 public declarations, meaning one of his supporters was being publicly misleading about who they voted for, or Mrs May – who has never publicly expressed her intentions – must have backed someone else.

Conservative party leadership contender Boris Johnson arriving for the Conservative National Convention meeting at the Park Plaza Riverbank Hotel, central London, today

Mr Stewart was one of Mrs May's final appointments to her Cabinet and had been one of the most ferocious defenders of her Brussels deal. He has also said he would not seek major changes to Mrs May's Withdrawal Agreement that has been comprehensively rejected by the Commons three times.

Instead Mr Stewart has said he would seek to 'communicate' the deal in a better fashion, and, like Mrs May, has vowed to avoid a No Deal scenario at all costs. A senior Tory told The Mail on Sunday: 'At the end of the day Mrs May believes the only way to leave is with a deal and Rory is the only candidate really sticking to that.'

Another ally added: 'No one has asked her but she values loyalty, and while he was quick out the traps in saying he wanted to run, Rory spent most of the year defending her.'