London's Metropolitan Police Service was put in a special monitoring and improvement program by a watchdog on Tuesday and told to come up with an improvement plan after criticism over its handling of a string of high profile cases.

Her Majesty’s Inspectorate of Constabulary and Fire & Rescue Services said in a statement that the Met was being monitored through its "Engage" process.

The process "provides additional scrutiny and support to help it make improvements," the watchdog said. The statement did not detail what had triggered the move.

"A series of appalling scandals have not only exposed deep cultural problems but have damaged the confidence of Londoners in the capital’s police service," the Mayor of London, Sadiq Khan, said in a statement.

"The decision by the HMIC to now move the Met into special measures has laid bare the substantial performance failings by the force."

The force was shaken last year by the abduction, rape and murder of a woman, Sarah Everard, by one of its officers. Its policing of a vigil for the victim was later found to be unlawful by a London court and it has been beset by revelations of a culture of bullying, racial discrimination and misogyny.

The Met said it recognised the cumulative impact of events and problems it faced.

"We are determined to be a police service Londoners can be proud of. We are talking to the Inspectorate about next steps," it said in a statement.

In February, London police chief Cressida Dick resigned after Khan told her he was not satisfied she could root out the problems that existed within the force.

Her successor has yet to be appointed.

The watchdog's website sets out that the "Engage" process is used when a force is not responding to a cause of concern, or is not successful in addressing it. (Reuters)