Finance Minister Rishi Sunak and Health Secretary Javid highlighted concerns about the leadership in their resignation letters.

Sunak, the now former chancellor of the exchequer, said "the public rightly expect government to be conducted properly, competently and seriously".

"I believe these standards are worth fighting for and that is why I am resigning," he said.

He also hinted at splits on economic policy, with a planned joint speech with the prime minister making it clear "our approaches are fundamentally too different".

Javid said the public had concluded that under Johnson the Conservative Party were not "competent in acting in the national interest".

* WHY NOW?

Johnson's judgment has once again been called into question over his handling of the Chris Pincher row.

The former deputy chief whip quit last week after he "drank far too much" and "embarrassed myself" at the exclusive Carlton Club, where he allegedly assaulted two male guests.

The prime minister was forced into a humiliating apology after admitting he knew about previous inappropriate behaviour by Pincher when he was a foreign office minister in 2019 but still appointed him to a senior government role.

* ANY OTHER CAUSES OF CONCERN?

Plenty. Last month, 41 per cent of Conservative MPs said they had no confidence in Johnson, with issues including his personal style, economic policy and a scathing report into lockdown-busting parties at his Downing Street offices.

Some were prepared to back Johnson, who led the party to a landslide election win in 2019, because of his popularity with voters.

But recent by-election defeats, which led to the resignation of party chairman Oliver Dowden, cast doubt on Johnson remaining an electoral asset to the party.

* WHAT NEXT FOR SUNAK AND JAVID?

Both have leadership ambitions and are in a position to inflict further wounds on the prime minister.

As resigning ministers they have the opportunity to make statements in the House of Commons explaining their reasons.

* IS IT JUST THE USUAL SUSPECTS THAT JOHNSON NEEDS TO WORRY ABOUT?

MP Jonathan Gullis, previously a Johnson loyalist, resigned as a ministerial aide.

"For too long we have been more focused on dealing with our reputational damage rather than delivering for the people of this country and spreading opportunity for all, which is why I came into politics," he said.

* SO IS THIS THE END?

It is a matter of days since Johnson said he was looking ahead to a third term in office which would keep him in No.10 into the 2030s, so resigning does not appear to be on his mind.

Unless the remaining cabinet ministers tell him the game is up, the main source of danger for the prime minister may be another attempt by backbenchers to oust him.

For that to happen, the rules will need to be changed to allow a second confidence vote within 12 months.

* CAN HE SURVIVE?

Under normal political rules, a prime minister in Johnson's position would probably already be calling the removal vans to Downing Street.

But he has made a career out of defying political gravity and still has a comfortable parliamentary majority.

Former prime minister and Conservative leader David Cameron described Johnson as a "greased piglet" and the current incumbent in British politics' top seat may yet find a way to save his bacon.

Australian Associated Press