Rishi Sunak said he is not prepared to “demonise” Boris Johnson and insisted the Prime Minister’s controversial former aide Dominic Cummings has “absolutely nothing” to do with his leadership campaign.

Mr Sunak kicked off his launch event in London by defending his former boss, saying that while Mr Johnson was “flawed” and that he had often disagreed with him, he had a “good heart”.

“I will have no part in a rewriting of history that seeks to demonise Boris, exaggerate his faults or deny his efforts,” he told an animated crowd of supporters and media.

Mr Sunak said he will run a “positive campaign” and refuse to “engage in the negativity you have seen and read in the media”.

It comes as the former chancellor has come under fire from allies of Mr Johnson, who believe his resignation last week helped spark the mass exodus of ministers which forced Mr Johnson to admit his time is up.

Mr Sunak said his decision to quit was “incredibly difficult and sad”, but “there were just some things that were becoming too difficult for me to keep working with him on”.

Mr Sunak also denied rumours Mr Cummings is secretly advising him and insisted they have not spoken since the former aide left No 10.

“Dominic Cummings has had absolutely nothing to do with this campaign and will have absolutely nothing to do with any government that I’m privileged to lead”.

“For the record, I’ve not communicated with Dominic Cummings since the day he left Downing Street”.

Mr Sunak, who has the most public declarations of support from Tory MPs of any candidate so far, said he is encouraged by the “breadth of support” from all wings of the Tory party, saying it will enable him to bring the party back together and “reunite the country”.

Apart from supporters holding blue placards emblazoned with his campaign slogan “ready for Rishi” and “reunite the country”, the audience also featured Transport Secretary Grant Shapps, who had just folded his own leadership campaign to back Mr Sunak.

Oliver Dowden, who stepped down as party chairman after the Tories’ recent double by-election defeat, and former chief whip Mark Harper were also there.

Deputy Prime Minister Dominic Raab introduced the leadership hopeful at the event by taking a swipe at his rivals.

“While others talk the talk, Rishi this month delivered the biggest tax cut for working people in a decade,” Mr Raab said.

“There is no time to learn on the job”.

Mr Sunak also took aim at his rivals, whose tax plans, he suggested, are “not credible”, and who want to reverse Government decisions they previously supported.

He used his campaign launch to brandish his “traditional Conservative values” of “hard work, patriotism, fairness, a love of family, pragmatism, but also an unshakable belief that we can build a better future”.

On defence spending, he would not commit to the “arbitrary target” of spending 2.5% of national income on the budget as he said his approach would be “threat-based”.

Mr Sunak took questions from only one Tory councillor and four journalists, attempting to end the session after being quizzed over the recent controversy about his wife’s non-domiciled status for tax purposes and the US green card he held while serving in Government.

Asked whether he would be dogged by these problems as prime minister, he said: “They’re all out there and we’ve discussed them and we addressed them”.

The question was met with loud jeers and laughter from supporters.