Boris Johnson is battling for survival but continues to face criticism from his own party.

So how could MPs take steps to force him out of office? Political Editor Paul Francis sets out the possible ways.

It was just four weeks ago that MPs voted in a secret ballot that allowed Boris Johnson to keep his job.

The vote of confidence was triggered after more than 54 MPs wrote to formally request the ballot take place.

He made it through with a majority of just 63 votes - 211 for and 148 against.

Despite the victory, questions over his leadership have not disappeared and with around 30 ministers resigning from their post in less than 24 hours many think it's only a matter of time.

But how?

One option could be to force a second vote of no confidence in the party leader. Current rules do not permit another challenge if the incumbent leader of the Conservative Party has survived one such vote in the preceding 12-months.

However, the 1922 committee - often referred to as the men in grey suits - can choose to change the rules. That would open the door to a second vote.

Another possibility is that party chiefs go to the PM to say that he has lost the confidence of the party and encourage him to step down voluntarily rather than force a contest.

This method was used to persuade Teresa May to relinquish the role. One advantage of this route is that it would avoid blood on the carpet and would be less divisive.

Another way to persuade Boris to step aside would be for constituency associations to write to the 1922 committee to formally call for a vote among activists about the leader.

There is also the possibility of rebel MPs backing a call by opposition parties for a vote of no confidence.

If Labour were to make such a call for a debate and no confidence vote, Conservative MPs could defy their own party.