The former chancellor defended the prime minister, calling him "one of the most remarkable people I have ever met", despite resigning last week over Mr Johnson's conduct in office.

Fellow contenders Tom Tugendhat and Kemi Badenoch officially launched their bids at the same time, with Mr Tugendhat pledging to cut fuel duty by 10p and Ms Badenoch refusing to enter into a tax cut "bidding war" against the other candidates.

Politics Hub: Johnson loyalists to back 'stop Rishi' candidate

Addressing the issues around Mr Johnson in his speech, Mr Sunak said: "Did I disagree with him? Frequently. Is he flawed? Yes and so are the rest of us. Is it no longer working? Yes and that is why I resigned.

"[But] I will have no part in a history that seeks to demonise Boris."

It comes as former Conservative Prime Minister John Major criticised ministers for not speaking out against Mr Johnson, saying he had "damaged our country at home and overseas and I think has damaged the reputation of Parliament as well".

He added: "They were silent when they should have spoken out and then spoke out only when their silence became self-damaging."

Asked by Sky News' Beth Rigby if he accepted he was seen as "corrosive" by many Tory MPs after his support for Mr Johnson - and sudden withdrawal of it - as well as previous issues around his wife's tax affairs, Mr Sunak insisted he had backing from "all wings of the party".

He continued: "That's why I believe I am best placed to bring the party back together, but also reunite the country, because ultimately, that's the most important thing."

The main thrust of his pitch, however, was a promise to "steer our country through these headwinds" of a tough economy, adding: "Once we have gripped inflation, I will get the tax burden down. It is a question of when, not if'."

Mr Sunak made his bid with the support of Deputy Prime Minister Dominic Raab and Transport Secretary Grant Shapps, who dropped out of the race moments before Mr Sunak's launch event began.

Opening the event, Mr Raab said: "I know that Rishi has got what it takes… to provide the leadership that we need to steer the country through tough economic times."

Read more: Tory leadership contests - beer, brownies, smoothies - and dirty tricks

The eight contenders who have made it through to the next round, after getting the backing of at least 20 MPs, were revealed at 6pm on Tuesday.

They are:

• Rishi Sunak
• Penny Mordaunt
• Tom Tugendhat
• Liz Truss
• Suella Braverman
• Jeremy Hunt
• Kemi Badenoch
• Nadhim Zahawi

Voting by other Conservative MPs to whittle down the first-round candidates will take place on Wednesday, with candidates then needing 30 backers to get through to the second round.

Those candidates will face successive rounds of voting from Thursday - and most likely until the end of next week - until there are only two left.

About 160,000 Conservative Party members will then vote for their favourite and the result is to be announced on 5 September.

Mr Johnson will remain in Number 10 acting as a caretaker prime minister after announcing his departure last week in the face of a raft of resignations over his handling of disgraced MP Chris Pincher.

Labour is attempting to oust the prime minister more quickly by calling a confidence vote in Parliament on Wednesday.

Speaking at his launch, Mr Tugendhat - who chairs the foreign affairs committee - said tax cuts can't be the only issue for the next leader to tackle, adding: "When our service is most needed, we have retreated - we have retreated into the pettiness of politics that is more about personality than principle.

"We have retreated into division when we desperately need unity. When our nation needed our party to function, we retreated into faction. When the moment demanded service, we delivered scandal.

"We should not accept retreat. We must return to service."

In her bid to be the next Tory leader - and prime minister - former equalities minister Ms Badenoch promised a restructure of Whitehall to deliver on the party's commitments.

"We can only deliver lower taxes if we stop pretending that the state [should] continue to do everything we are trying to do," she said.

"We need to recognise it is not about trying to do the same with less. We need to focus on the essentials, we need to be straight with people - the idea we can simply say 'efficiency savings', click our heels three times and it will materialise is for the birds.

"It is the scale and structure of government that drives the inefficiencies. My government will discard the priorities of Twitter and focus on the people's priorities."

The 'stop Rishi' candidate?

After this morning's cabinet meeting in Number 10, both Brexit opportunities minister Jacob-Rees Mogg and Culture Secretary Nadine Dorries announced their backing for Liz Truss as the party's next leader.

They described the foreign secretary as a "strong Brexiteer" and someone who had spoken out against tax rises.

Rigby said that by coming out for Ms Truss, the influential pair were signalling to the right of the party that she was "the stop Rishi candidate".

Asked by reporters if that was the case, Mr Rees-Mogg did not deny it, merely replying: "She is the best candidate."

Meanwhile, senior backbencher David Davis gave his backing to former Defence Secretary Penny Mordaunt, who is leading the Conservative Home poll of party members on who they want as their next leader.

He told Rigby: "We need high integrity - we can't afford any more scandals after the last two years - [and] she is a woman of incredible integrity."

Sky News is hosting a live TV debate with the contenders vying to be the next leader of the Conservative Party and therefore prime minister, and you could be in the virtual audience.

The debate will take place on Monday 18 July hosted by Sky News presenter Kay Burley.

If you would like to be a member of the virtual audience and be in with a chance of asking a question, please email This email address is being protected from spambots. You need JavaScript enabled to view it..