The Mayor of London, Sadiq Khan, has lodged an application for a judicial review of the decision to free rapist John Worboys.
The Labour politician said he lodged an application following the decision of the Parole Board.
In a statement, he said: “It was an astonishing and deeply concerning decision that simply cannot go unchallenged. For victims, and all Londoners, it must be properly scrutinised in the courts. The Chair of the Parole Board has welcomed this scrutiny.
“I will always put the safety of Londoners, and the needs of victims, first – which is why I instructed leading counsel to begin this process last week.
“Londoners need to know that those in authority are doing everything they can to keep them safe, and that means keeping dangerous individuals off our streets.”
The move comes following criticism of the Parole Board’s decision to approve 60-year-old Worboys’ release later this month, following his minimum eight-year term.
The former black cab driver was jailed indefinitely in 2009 for drugging and sexually assaulting female passengers.
He was convicted of 19 offences relating to 12 victims but is suspected to be linked to a total of 102 complaints.