Boris Johnson is launching his bid to seize the Tory crown, as a cross-party alliance of MPs attempts to use Commons procedure to block a no-deal Brexit.
The former foreign secretary has emerged as the clear frontrunner in the race to succeed Theresa May – despite so far staying largely silent in the contest.
For many MPs, he is the one candidate who can see off the twin threats of Nigel Farage’s Brexit Party and a Labour government led by Jeremy Corbyn.
However he remains a divisive figure within the party, with criticisms over his role in the Vote Leave campaign and his record as foreign secretary.
Ahead of his launch event in London on Wednesday, leading supporter Treasury Chief Secretary Liz Truss insisted he had done a “brilliant job” at the Foreign Office.
She brushed off criticism that he had been responsible for the continuing imprisonment of the British-Iranian mother Nazanin Zaghari-Ratcliffe in Iran.
“I think it’s a sign – that he is being attacked shows the huge public appeal he has, the huge power he has to communicate,” she told the BBC Radio 4 Today programme.
“His record is of being the most successful mayor of London we have had, of being an excellent foreign secretary.”
Mr Johnson is expected to use his leadership launch to again insist Britain must quit the EU by October 31.
“We simply will not get a result if we give the slightest hint that we want to go on kicking the can down the road with yet more delay,” he is expected to say .
“Delay means defeat. Delay means Corbyn. Kick the can and we kick the bucket.”
Meanwhile there was anger among Brexiteers at the latest move by MPs opposed to no-deal to seize control of Commons business from the Government.
Labour is using an opposition day debate to try and give control of the Commons agenda to MPs on June 25 in order to stop the UK exiting the EU without a deal in the autumn.
Prominent Brexiteer Sir Bill Cash strongly attacked supporters of the move who include Tory former minister Sir Oliver Letwin, plus the SNP, the Liberal Democrats, Plaid Cymru and the Greens.
Sir Bill told the Press Association: “They are causing a breakdown of our democracy.”
With the Labour-led motion only needing a relatively small number of Tory MPs to support it for success, Sir Bill, who supports Mr Johnson, was scathing about the involvement of Sir Oliver, a Michael Gove backer in the leadership race.
Sir Bill said: “He has put his name to an opposition day motion with Marxist Jeremy Corbyn.”
But shadow Brexit minister Jenny Chapman said the vote on blocking a no-deal Brexit was a “safety valve” aimed at Tory leadership contenders trying to freeze MPs out of the decision.
She told the Today programme: “This is about that safety valve, that lock in the process, so that somebody who may find themselves elected a leader of the Tory Party on a promise of, in Dominic Raab’s case, proroguing Parliament, and locking Parliament out of this process – they can’t do that.
“They would have to come back to Parliament and get the consent of MPs.”
The looming Commons vote forced fellow leadership contender Sajid Javid to push back the time of his leadership launch for later on Wednesday.
The Home Secretary is expected to tell the gathering: “I believe now more than ever that this is a moment for a new kind of leadership and a new kind of leader.
“A leader is not just for Christmas, or just for Brexit.
“So we can’t risk going with someone who feels like the short-term, comfort zone choice.
“We need tomorrow’s leader, today.”