Boris Johnson has exacted revenge on his former ally Michael Gove, by backing energy minister Andrea Leadsom as the next prime minister.
The endorsement damages Mr Gove's chance of reaching a run-off for the leadership of the Conservative party, and further establishes Mrs Leadsom, a former banker with no cabinet experience, as a serious rival to the frontrunner Theresa May.
"Andrea Leadsom offers the zap, the drive, and the determination essential for the next leader of this country," said Mr Johnson, who abruptly withdrew from the race last Thursday after discovering Mr Gove had turned against him. "She has a better understanding of finance than almost anyone else in Parliament."
A ConservativeHome poll of party activists gave Mrs Leadsom 38 per cent support, compared with Mrs May's 37 per cent.
On Monday Mrs Leadsom warned that she will turn her sights on City excess if she reaches Number 10.
She launched her "Fresh Leadership" bid with a promise to try to heal divisions in Britain exposed by the EU referendum, with any future tax cuts focused on the lowest paid.
Deflecting criticism of her financial arrangements and the use of trusts, Ms Leadsom declared: "The richest people of Britain should know that they will not be my priority.
"Those people who have become rich by winning boardroom pay rises that bear no relation to company performance should be aware that I find this unacceptable," she said, without explaining how she would curb them.
She also bemoaned the fact that "too few in my old field of financial services were ever brought to book for their part in the 2008 crash", suggesting she favours tougher sanctions against wrongdoing in the City.
The 53-year-old energy minister was feted by Eurosceptic Tory MPs at the launch at a Westminster club. Iain Duncan Smith, former cabinet minister, declared that she was "the real deal".
Meanwhile Peter Lilley, another former minister, said: "She has drive without the acerbity of some driven people. She doesn't have the acerbity that some people associated with Mrs Thatcher."
One MP said: "[Mr Johnson's endorsement] won't have an impact among MPs. It may have an impact among the membership."
Like Mr Gove, Mrs Leadsom nearly backed her fellow Brexit campaigner Mr Johnson before deciding to run herself. She reportedly backed away after some confusion over his omission to confirm that she would receive a top job.
She hopes to reach the final shortlist of two with Mrs May, giving Tory activists a choice between two women to follow in the steps of the Iron Lady as Britain's second female prime minister.
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Some Treasury officials have said that Mrs Leadsom was a "disaster" during her brief stint as City minister, but she shrugged off the anonymous criticism: "They should come and talk to me about it," she said.
The criticism focused on her alleged inability to command a brief or to make decisions, but one supporter of Mrs Leadsom said: "They would say that — they just didn't like being told what to do."
Mrs Leadsom may yet find herself in the sweet spot of the Tory leadership contest, with her pro-Brexit background and her call for a softer style of Conservatism to unite a divided country.
She drew attention to the charities she set up to help parents bond with their children in their early years, and criticized Mrs May for treating the future of EU nationals living in Britain as "a bargaining chip" in Brexit negotiations.
The former Treasury minister declared that she would start Article 50 exit negotiations with the EU as soon as possible and said the party should elect a leader who campaigned for Brexit.
"The person to take the country forward should be someone who believes in the opportunities outside the EU," she said, amid signs that she is starting to pull in support from Tory Brexit campaigners.
The campaigns of the other two Brexiters — Liam Fox and Michael Gove — have so far failed to ignite, while Boris Johnson dropped his leadership bid last week after Mr Gove sabotaged his campaign.
Stephen Crabb, the new work and pensions secretary, is the fifth candidate and is standing on a "blue-collar" Conservative ticket. On Monday he became the first candidate to commit himself to building a third runway at Heathrow.
Tory MPs will begin whittling down the candidates on Tuesday to a shortlist of two. According to Channel 4 last night's tally of supporters showed: May 120; Leadsom 37; Gove 31; Crabb 24; Fox 13; not known 106
Although both Mrs May and Mrs Leadsom would appeal to a sense of Thatcherite nostalgia among the 125,000 party members, it is the latter who appears most aligned to their Eurosceptic views.