The endorsement from David Lidington, who as Cabinet Office minister is Theresa May’s effective deputy, is a major coup for the International Development Secretary and boosted speculation last night that Mr Stewart could survive into the next round.
Candidates who secure 33 votes and avoid coming last in today’s second ballot of Tory MPs will take part in a live TV debate on the BBC, which Mr Johnson has agreed to join after being ‘empty chaired’ by Channel 4 on Sunday night.
Criticism of the former foreign secretary intensified after he also failed to attend a hustings event yesterday where all five other candidates took questions from Westminster journalists. Endorsing Mr Stewart at a rally across the Thames from Parliament yesterday evening, Mr Lidington said: “I think that there is a yearning in this country for political leaders who tell it straight to people, who are honest about the difficulties and challenges that lie ahead, as well as the policies and the remedies that they are proposing.
“And I also think that there is a yearning in this country for political leaders who are willing to listen, who are prepared to get out of the comfort zone and out of the Westminster bubble.”
The Prime Minister repeated her refusal to publicly support any candidate when asked by journalists yesterday, but Mr Stewart has said he is not seeking to renegotiate her Brexit deal and Mr Lidington’s comments will be seen as further advancing the cause of the Scottish MP.
At the hustings, Mr Stewart said he had the necessary 33 backers to make it through the second round of voting in the contest “if they do what they say”.
The international development secretary, who has been fiercely critical of Mr Johnson, suggested that he was the one to beat the runaway favourite – and accused the former foreign secretary of making different promises to different MPs over his Brexit policy.
“Who is going to be nimble enough, who has the style, who has the approach, who has the way of dealing with the public – I don’t think the answer is going to be pre-scripted answers,” he said.
Securing a place in tonight’s BBC debate would represent a huge victory for Mr Stewart, who scraped through the first ballot of MPs with 19 votes.
As well as the endorsement from Mr Lidington, the Stewart campaign picked up momentum yesterday by winning the public backing of three other MPs, including the Scottish Tory Paul Masterton.
Mr Masterton broke with Matt Hancock, whom he had supported before the health secretary dropped out of the race.
Mr Hancock backed Mr Johnson to be the next prime minister in a blow to the leadership hopes of Michael Gove, who had been courting the support of his friend.
Mr Hancock said the former foreign secretary was now the best candidate to re-unite the fractured Conservative Party despite previously having ruled out a no-deal Brexit, in contrast to Mr Johnson.
In a veiled reference to reports suggesting that Mr Hancock could have his sights on 11 Downing Street under a Johnson premiership, justice secretary David Gauke, who is supporting Mr Stewart, said: “If Boris wins, good luck to whoever becomes his chancellor. It would be a noble act of self-sacrifice to accept the job. Who’d do it?”
Home secretary Sajid Javid, who won 23 votes last week, also claimed he was “extremely confident” of getting through. Mr Javid said he should be put through to the vote of party members to decide between the final two candidates because of his different background.
“I think there is a growing feeling in the party that when we get to the final two, we should have a robust debate between two credible change candidates,” he said. “If we don’t get change, people will vote for change in the form of Jeremy Corbyn.”
The position looks more difficult for former Brexit secretary Dominic Raab, who is competing with Mr Johnson for Brexiteer votes. At the hustings, Mr Raab hit back at criticism over his refusal to rule out proroguing Parliament to deliver a no-deal Brexit, arguing that suspending the Commons was a “central plank” of Mr Stewart’s plan for another vote on the existing deal with the EU because of a ruling from Commons Speaker John Bercow.
Mr Raab also defended his record in government, saying Brexit negotiations broke down “because ultimately the Prime Minister and the Cabinet were not willing to hold the line”.
He said he would implement “proper managerial oversight” of civil servants, who would not just be listened to.
The current number two in the race, Jeremy Hunt, stood out as the only candidate who appeared to endorse US president Donald Trump’s sharing of comments attacking London Mayor Sadiq Khan on Twitter.
The foreign secretary said he agreed “150 per cent” with the “sentiment” of the Katie Hopkins’ comment, despite the tweet being labelled racist for referring to ‘Londonistan’.
Mr Javid said supporting the comments was “unbecoming” of a US president and “he should stick to domestic politics”.
After the hustings, Mr Stewart tweeted: “I 100% disagree with both the language and the sentiment of the last sentence of this tweet. Can all candidates please confirm the same.”
Mr Hunt also said he did not regret previously likening the EU to the USSR in a speech at the Tory Party conference last year, saying: “I think it showed I’m prepared to say things to friends they might not like and able to continue a relationship even saying those uncomfortable things.”
Meanwhile, Philip Hammond said he was disappointed Rory Stewart was the only candidate who had committed to meet existing rules on the public finances.
The Chancellor had called on all the leadership contenders to sign up to a pledge to keep the deficit falling.
Speaking at an event in the City of London, he said: “It is a disappointment to me that only one of the candidates remaining in the race, Rory Stewart, has actually signed up to that pledge.
“I would urge the other candidates to do so, to reassure the public that our hard-won reputation for fiscal responsibility is not going to be squandered.”