Liz Truss maintained she is a "loyal person" as she batted questions over her support for Boris Johnson during her campaign launch to replace the Tory leader.
At a speech in central London, the Foreign Secretary said she would be ready from "day one" as prime minister to continue the government's levelling-up plans and "lead the free world" against Russian president Vladimir Putin.
The Foreign Secretary has the support of Mr Johnson’s remaining loyalists in an increasingly competitive and sometimes fractious Tory leadership race that will select his successor.
On Thursday morning, allies of Ms Truss seized on scathing comments made by former Brexit minister Lord Frost, who described frontrunner Penny Mordaunt as a "problem" and said he felt she did not "master detail" over their time working together during negotiations with the EU.
Setting out her own pitch, Ms Truss insisted she is a “loyalist” when quizzed on why she had not quit Mr Johnson’s Cabinet amid a series of damaging scandals.
“I am a loyal person, I am loyal to Boris Johnson, I supported our prime minister’s aspirations,” she said, although she also promised a change of tack on the economy and to reverse the planned rise in national insurance.
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Ms Truss dodged questions about worries she could be outflanked by rival Ms Mordaunt - tipped as the favourite in an exclusive poll on ITV's Peston show - instead stressing the "wide array of talent" the leadership contest is displaying.
While she said she would not disparage other candidates, Lord Frost's blunt attack on Ms Mordaunt was highlighted by the Truss campaign, with Treasury Chief Secretary Simon Clarke describing his warning as a "really serious one."
Lord Frost told TalkTV she lacked a grasp of the detail, was unwilling to deliver tough messages to Brussels, and that he had to ask Boris Johnson to replace her.
“I would not feel able to serve in a ministerial team under Penny Mordaunt. That’s how strongly I feel about that. I felt I had to make that clear today. MPs are voting today and I think they need to know the facts," he said.
Lord Frost continued: “I am quite surprised at where she is in this leadership race. She was my deputy – notionally, more than really – in the Brexit talks last year.
“I felt she did not master the detail that was necessary in the negotiations last year. She wouldn’t always deliver tough messages to the European Union when that was necessary.
“She wasn’t fully accountable, she wasn’t always visible. Sometimes I didn’t even know where she was.
"This became such a problem that, after six months, I had to ask the Prime Minister to move her on and find somebody else to support me.”
Ms Mordaunt's team did not engage with Lord Frost's comments, instead talking about her "respect" for the former minister and insisting she will "always" stick up for Brexit.
Ms Truss, meanwhile, continued with her pitch to the her party, saying she did not have a conventional Tory background but promised to deliver Conservative values while in office.
“I will campaign as a Conservative and I will govern as a Conservative,” she said. “I am ready to be prime minister from day one.”
She opened her speech with a clear message: “We are at a critical moment for our country.”
“Now is the time to be bold, we cannot have business-as-usual economic management, which has led to low growth for decades.”
To shouts of “hear, hear”, she said that it was time to deliver on Brexit and “win the fight for freedom, at home and abroad.”
She secured her place in the next round of the contest by nabbing the third-highest number of votes in the first ballot of Tory MPs on Wednesday, behind rivals Rishi Sunak and Penny Mordaunt.
Ms Truss’s backers have been accused of running a campaign to damage Mr Sunak’s chances in the contest, criticising the former chancellor’s “economically damaging” policies.
In her campaign speech, Ms Truss detailed her economic plan, which includes reversing April’s National Insurance rate rise, lowering corporation tax and enacting supply-side reforms.
The former-Remainer-turned-ardent-Brexiteer’s hard line on Ukraine, insisting Russian forces must be driven from the country, and threats to tear up parts of the Northern Ireland Protocol with the EU play well with sections of the party.
At least one candidate will be eliminated from the contest on Thursday as the second round of voting gets unrderway.
Under the contest's rules, any MP who receives fewer than 30 nominations would be ruled out. If all reach the threshold, then the candidate with the least support would drop out.