We're now hearing that Universities Minister Michelle Donelan has gone into No 10, shortly after Nadhim Zahawi.

As we've been reporting, Johnson has also written a letter to former health secretary Sajid Javid - the first cabinet member to resign.

In his letter Johnson says: "Thank you for your letter this evening tendering your resignation. I was very sorry to receive it."

Johnson commends Javid for his work as health minister during the Covid pandemic.

He adds: "You will be greatly missed, and I look forward to your contribution from the backbenches."

A fourth PPS, Virginia Crosbie, has resigned this evening. She was a parliamentary aide in the Wales Office.

She says in her resignation letter that if Boris Johnson continues as PM he risks "irrevocably harming this government, and the Conservative party and will hand the keys of Downing Street to a Labour Party unfit to govern".

Image source, Avalon

In a letter to former chancellor Rishi Sunak, UK Prime Minister Boris Johnson says he is sorry to receive Sunak's letter resigning from the government.

He says Sunak provided "outstanding service to the country through the most challenging period for our economy in peacetime history".

He mentions the furlough scheme Sunak coordinated during the height of the Covid pandemic and says Sunak's efforts "primed the economy for a rapid recovery once the immediate dangers of the pandemic receded".

Johnson adds "I have enormously valued your advice and deep commitment to public service and will miss working with you in government".

Prime Minister Boris Johnson has been sending letters to both Rishi Sunak and Sajid Javid.

In his letters, Johnson told the former chancellor and former health secretary he was sorry to see them resign.

Nicola Richards MP, a parliamentary private secretary in the Department of Transport, quits her role in government.

In her letter of resignation, Richards describes the Conservative Party as "currently unrecognisable."

It makes her the third parliamentary aide to quit in the wake of Javid and Sunak's shock resignations in the last hour.

Earlier Saqib Bhatti MP and Jonathan Gullis MP - both parliamentary private secretaries - also quit their posts.

They were followed by Bim Afolami MP, a vice-chair of the Conservative Party, who resigned live on television.

We're hearing Steve Barclay will replace Sajid Javid as Health Secretary, according to Whitehall sources.

Education Secretary Nadhim Zahawi has just gone into No 10 Downing Street.

He is one of the few cabinet members not to have expressed his support for Prime Minister Boris Johnson following Sunak and Javid's resignation.

Conservative MP Andrew Bridgen has told the BBC the PM "should do what he should have done some time ago, and resign".

"If he doesn't do that, the party will have to force him out."

He said ideally other members of the Cabinet should resign and "make their position clear" - but if not, he said, it would be down to the 1922 Committee to elect an executive who would be willing to change the rules - thereby triggering another vote of confidence in the prime minister.

"I confidently predict that Boris Johnson, one way or another, will be removed before summer recess."

He described watching junior ministers being pushed out to defend the PM's line on Chris Pincher that he wasn't aware of his background was "the straw that broke the camel's back".

He added that Cabinet ministers were only now catching up with many backbenchers' belief that Johnson "is an existential threat to the Conservative party".

We've just been hearing a bit more from Labour leader Sir Keir Starmer. He calls for "a fresh start" in leadership for the UK, adding that he would support the calling of a general election.

Starmer says Tory cabinet ministers have been complicit with Prime Minister Boris Johnson, while he "disgraced his office and let down his country".

"The Tory party is corrupted, and changing the man at the top won't fix it. We need a real change of government and a fresh start for Britain", he says.

Former Brexit minister Lord David Frost has released a statement to say that Rishi Sunak and Sajid Javid did "the right thing this evening".

He says Boris Johnson has "huge achievements to his credit" and "a place in history for delivering Brexit and much more".

"But it is now time to look forward," the man who worked very closely with the prime minister before resigning at the end of last year said.

"The interests of the country, our new-found self-government, and the Conservative Party would be best served by a new leadership and a new prime minister."

As we told you earlier, Bim Afolami has resigned as vice-chair of the Conservative Party. We have a bit more detail now about what he said when he did so live on television.

Speaking to Talk TV, Afolami called on Boris Johnson to resign as prime minister after losing "the support of the party and the country" following the exit of Sunak and Javid.

The Conservative MP for Hitchin and Harpenden since 2017 said he could no longer serve under Johnson.

Saqib Bhatti, parliamentary private secretary to now former health secretary Sajid Javid, has also resigned.

In a statement on Twitter, he said: "The Conservative party has always been the party of integrity and honour but recent events have undermined trust and standards in public life."

Jonathan Gullis, PPS to Northern Ireland Secretary Brandon Lewis, has also quit. He said for too long "we have been focused on dealing with our reputational damage rather than delivering for the people".

Culture Secretary Nadine Dorries says she is "100%" behind Boris Johnson, adding he "consistently gets all big decisions right".

Brexit Opportunities Minister Jacob Rees-Mogg also insists the PM can stay in office: “Over the centuries members of the Cabinet have come and gone and prime ministers who have a majority in the House of Commons are able to continue.”

Asked if it's a leadership pitch by Rishi Sunak and Sajid Javid to resign, he adds: "You might think that, I couldn’t possibly comment.”

Scottish Secretary Alister Jack says: “I fully support the prime minister. I am sorry to see good colleagues resign, but we have a big job of work to do, and that’s what we’re getting on with.”

Boris Johnson loyalist Jacob Rees-Mogg is speaking to Sky News.

He says "there is no other leader I would want to fight a general election under" as he provides backing for the prime minister.

He says he met Boris Johnson tonight after the resignations of Sajid Javid and Rishi Sunak and the prime minister's mood was very much "business as usual".

Rishi Sunak says he can no longer serve as chancellor because his approach has become "fundamentally too different" from Boris Johnson's.

In his shock resignation letter he says:

Image source, Rish Sunak

You can read the letters from Sunak and Javid in full here

Betting firm Ladbrokes Politics have just suspended betting on "when will Boris Johnson be replaced as prime minister?"

They have also tweeted, external that the odds have shortened to 7/1 (from 12/1) on a general election being held this year.

Image source, Reuters

We have more reaction to news of this evening's double resignation in Westminster, this time from Scottish First Minister Nicola Sturgeon, who says "the whole rotten lot" in Boris Johnson's government should go.

"Feels like [the] end might be nigh for Johnson - not a moment too soon," she tweeted, external.

"Notable [though] that the resigning ministers were only prepared to go when they were lied to - they defended him lying to public.

"The whole rotten lot need to go. And [Scotland] needs the permanent alternative of independence."

Andrew Murrison has resigned as Boris Johnson's trade envoy to Morocco.

The Conservative MP for South West Wiltshire has formally served as a minister for the Foreign Office and the now-defunct Department for International Development.

In his letter he said, "the last straw in the rolling chaos of the past six months has been the unavoidable implications of Lord McDonald's letter".

Lord McDonald, the former top civil servant in the Foreign Office, wrote to the Parliamentary Commissioner for Standards Kathryn Stone over No 10's statements on MP Chris Pincher, who last week resigned as a Conservative whip and was then suspended as a party MP over allegations he groped two men at a private members' club in London.

Murrison tweeted his letter calling on the prime minister to resign, external.