In her first broadcast interview since entering the Tory leadership race, Ms Truss also denied that her planned £30bn of tax cuts would increase inflation.

Speaking to BBC Radio 4’s Today programme, the Foreign Secretary was questioned about her own judgement in continuing to back Mr Johnson.

“I wanted Boris to carry on as Prime Minister. I think he did a fantastic job with the 2019 election, winning us a massive majority. He delivered Brexit, he delivered the vaccines.

Liz Truss addresses MPs that are supporting her bid for the Tory leadership.

“Regrettably, we got to a position where he didn’t command the support of our parliamentary party,” said Ms Truss, who grew up in Leeds.

“My judgment was that he admitted that he had made a mistake, or several mistakes, over the course of the last year, but the positive side of the balance sheet was extremely positive.”

Asked whether she is the continuity Johnson candidate, she said: “What I am not is the continuity economic policy candidate, because I think that is where we didn’t get it right.”

While Mr Johnson has not said publicly who he is supporting, he is understood to favour Ms Truss in the race to succeed him as Prime Minister. In his final speech at Prime Minister's Questions yesterday, he criticised the Treasury and called for the next Prime Minister to pursue tax cuts and deregulation in what was viewed as thinly-veiled criticism of his former Chancellor Rishi Sunak.

Ms Truss has vowed to bring in an emergency budget to swiftly axe the National Insurance rise if she wins the race to be the next Prime Minister as part of a tax cut plan that has been costed at around £30bn.

She told the BBC that tax plans would not increase inflation despite economists’ concerns.

“My tax cuts will decrease inflation,” she told BBC Radio 4’s Today programme.

“We have had a consensus of the Treasury, of economists, with the Financial Times, with other outlets, peddling a particular type of economic policy for 20 years. It hasn’t delivered growth.”

Ms Truss, a former Treasury chief secretary, said: “What I know about the Treasury, from having worked there, is they… do have economic orthodoxy and they do resist change.

“What people in Britain desperately need now is change. We need to unleash investment in our country, we need to get the EU laws off our statute books and be attracting more funds – for example from pension funds – into high-growth businesses.”

She said reducing National Insurance and cutting corporation tax “increases the supply side of the economy”.

“The reason we have inflation is it’s a supply shock, combined with a slightly loose monetary policy over time.”

She added: “It’s not a gamble, it’s an economic reality that the higher taxes you have the more growth is choked off.”

Her position differs from that of Mr Sunak, who has said tax cuts cannot be introduced until inflation is "gripped" and who has accused leadership rivals including Ms Truss of peddling "fantasy economics" with their promises.

The pair will try to win over the support of local politicians today when they take part in a private hustings for the Conservative Councillors’ Association.

They will then tour the UK to take part in 12 hustings for the Tory members who will vote for their next leader, with the result being announced on September 5.

Mr Sunak argued that his rival, who is the bookmakers' favourite to win, would not be able to beat Labour leader Sir Keir Starmer at a general election.

“I’m confident that we can do that and we’ve got a really positive message to take out to all our members now – crucially, who is the best person to beat Keir Starmer and the Labour Party at the next election?” he said.

“I believe I’m the only candidate who can do that.”

Later writing in the Daily Telegraph, Mr Sunak tried to dial down the bitter attacks that have dogged the Westminster leg of the contest, saying Ms Truss is someone “I like and respect”.

He insisted he “will govern as a Thatcherite” after facing repeated criticism from the Tory right for wanting to hold off on tax cuts until after inflation is under control.

Ex-Roundhay pupil says she felt 'let down' like Liz Truss at Leeds school

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Liz Truss says she wanted Boris Johnson to continue as PM and denies £30bn tax cuts will fuel inflation