The mayor of London has thanked the outgoing Metropolitan police commissioner, Dame Cressida Dick, for four decades of “dedicated public service” on her final day in the role. Dick resigned following Sadiq Khan’s public criticism of her handling of a group of police officers based at Charing Cross police station who had shared racist, homophobic and misogynistic messages on WhatsApp. Other scandals, including the heavy-handed policing of a vigil for Sarah Everard, who was murdered by a serving Met officer, are thought to have contributed to the decision. Her resignation in February came just hours after she said she had no intention of quitting. In a statement, Khan said: “I would like to thank Dame Cressida Dick again for almost four decades of dedicated public service, with the vast majority spent at the Met, where she was the first woman to become commissioner. In particular, I commend her for the recent work in helping us to bring down violent crime in London.” He said he would not support the appointment of a new commissioner who “doesn’t understand or acknowledge the scale of the challenge facing policing”. “I’m now working with the home secretary on the recruitment of a new commissioner,” he said. “I’ve been clear that I won’t support the appointment of anyone who doesn’t understand and acknowledge the scale of the challenge facing policing. Regaining the trust and confidence of London’s communities is crucial to policing by consent and making our city safer.” Dick will take unused annual leave until her final day of official employment on 24 April. It is understood she will receive a severance payment of £166,000, the majority of which is related to a six-month notice period plus an additional payment of two months’ salary. On Friday Dick warned against the “politicisation of policing”, saying it was “a threat not just to policing but to trust in the whole criminal justice system”. “The current politicisation of policing is a threat not just to policing but to trust in the whole criminal justice system,” she wrote in a “letter to London”. “Operational independence from local and central government is crucial for an effective democracy and is a model respected around the world. We must all treasure and protect it.” The deputy commissioner, Sir Stephen House, will serve as acting commissioner while the recruitment process continues. It is expected to take up to five months.