Liberal Democrat leader Sir Ed Davey has said Boris Johnson must “publicly recuse” himself from involvement in the appointment of Dame Cressida Dick’s successor as Metropolitan Police commissioner because he is being investigated by the force.

He made the comments after the beleaguered Metropolitan Police boss resigned from her job having lost the backing of London Mayor Sadiq Khan.

But what exactly is the process for appointing a new commissioner, and would a Prime Minister ordinarily be involved?

Here are some key questions and answers.

– What will happen in the short term?

It has been agreed that Dame Cressida will continue to serve for a short period to enable an orderly handover.

It is not clear how long this period will be. It is understood that further detail will be communicated in due course.

– What is the normal process for appointing a Met commissioner?

The decision is made by the Home Secretary, currently Priti Patel. However, the mayor’s views should be taken into account.

On its website, the Met Police says: “Both have a role in appointing the Commissioner, with the decision taken by the Home Secretary following consultation with the Mayor.”

Sources close to City Hall gave a similar account of the procedure.

– So, does the Prime Minister have a say?

It is understood that the appointment of Dame Cressida’s successor will follow the formal process, whereby the Met commissioner is appointed by the Queen on recommendation by the Home Secretary, who has a statutory duty to give regard to the views of the Mayor of London.

It is also understood that the Prime Minister has no formal role in this process.

But Sir Ed’s comments raise questions over whether Mr Johnson should make clear that he will not be consulted on the decision.

It is not thought that Ms Patel anticipates the Prime Minister’s involvement in the process. The appointment of a Met commissioner is typically the Home Secretary’s decision to make.

Asked if the Prime Minister would ordinarily have a say, sources close to City Hall said the appointment was a decision for the mayor and Home Secretary.

Ms Patel thanked the outgoing commissioner for her service on Thursday night, but made no further comment about the appointment of her successor.

– What did Sir Ed say?

The Lib Dem leader said Mr Johnson must have “no role” in choosing the next commissioner, given the ongoing Met investigation into the so-called partygate scandal.

“A man under criminal investigation by the Met should not be able to choose who’s in charge of it,” Sir Ed said.

He added: “No-one handpicked by Boris Johnson would have the credibility needed for this big and important task. There must be no interference from No 10 in the appointment and Boris Johnson should publicly recuse himself from this decision.”