Scotland Yard's deputy commissioner Sir Stephen House revealed he has written to Ms Patel about the controversial circumstances of his boss's departure.

He claimed that "due process" was not followed over Dame Cressida's exit and expressed his "disappointment" and "surprise" at how her resignation came about.

In a shock announcement earlier this month, Dame Cressida revealed she would quit her role after losing the "confidence" of London mayor Sadiq Khan - although she will stay on for a "short period" while a replacement is appointed.

It came after the mayor said he was "not satisfied" with Dame Cressida's response to a damning report into the behaviour of officers at Charing Cross police station.

Mr Khan has denied claims that he issued an ultimatum to Dame Cressida demanding that she sack Charing Cross officers or face suspension herself.

But the Metropolitan Police Federation, which represents more than 31,000 officers, has since declared it has "no faith" in the mayor.

Appearing before the London Assembly's police and crime committee on Wednesday, Sir Stephen said he was "deeply disappointed" by the circumstances of Dame Cressida's resignation.

"It's been an extremely difficult couple of weeks for the Metropolitan Police Service and I can understand... many Londoners will have questions," Sir Stephen told assembly members.

"There's a clear procedure in statute laid down to allow the removal of a police chief officer.

"It's not been followed in this instance. It's not even been initiated in this instance.

"Due process has not been followed and instead we've seen matters played out in the media.

"Because of this, I've written to the home secretary to ask her to have a review carried out of the events that have taken place."

Sir Stephen also described himself and many fellow officers as "very surprised" at Mr Khan's loss of support for Dame Cressida.

"Only a few months ago the mayor was a strong advocate for a three-year extension for this commissioner," he added.

"Of course I know the indefensible messages exchanged by some police officers in Charing Cross police station have had an extremely powerful and toxic effect.

"I and my colleagues have read the content of those texts and been disgusted, as any right thinking person would be, by the content of them.

"We are all committed to rebuilding trust in the Met and we entirely recognise that this has been affected by this and other shocking events and cases."

The deputy commissioner argued that offensive messages exchanged by officers at Charing Cross police station "cannot have been a surprise" to Mr Khan.

"Mopac [the Mayor's Office for Policing and Crime] have been briefed on these events and they have been under investigation for four years," he told the committee.

"Only a few weeks ago, the mayor was a vocal supporter of the commissioner in a tripartite meeting with the home secretary. Hence my surprise at what's happened."

Sir Stephen added he felt "sad" for Dame Cressida that "her police career and lifetime of public services ended in this way".

"I know that I'm not alone in feeling this," he said.

Sources at City Hall dismissed Sir Stephen's claims about due process not being followed over the exit of Dame Cressida.

They suggested that Dame Cressida's decision to quit had removed the need for Mr Khan to follow the statutory process and pointed to the resignation of one of her predecessors, Ian Blair, as a precedent.

Lord Blair quit in 2008 after claiming to have lost the support of then London mayor Boris Johnson.

A spokesperson for Mr Khan said: "Trust in the police among Londoners has plummeted over the last two years and is now nearly at an all-time low following a series of devastating scandals involving police officers, including evidence of misogyny, racism, sexism, homophobia and bullying.

"The mayor is democratically elected by millions of Londoners and it is his job to hold the police to account - and he will continue to do so.

"The mayor is now working with the home secretary on the process to appoint a new commissioner at the Met, who understands the scale of the problem and who will take the necessary action to restore trust in the service."