The officer was shot by a man who was being detained at the Croydon Custody Centre in Windmill Lane at about 2.15am on Friday morning. Officers and paramedics treated him at the scene and he was taken to hospital by London Ambulance Service. But the officer later died in hospital.
The Met Police have launched a murder investigation.
The 23-year-old suspect was detained by officers at the scene.
He was also taken to hospital with a gunshot wound and remains in a critical condition, the Met said.
The suspect is believed to have turned the gun on himself after shooting the officer.
Commissioner Cressida Dick said: “This is a truly shocking incident in which one of our colleagues has lost his life in the most tragic circumstances. My heart goes out to his family, direct colleagues and friends.
“We are currently supporting his family and also have a dedicated team providing support to the officers and those in the custody centre who witnessed the shooting.
“When a colleague dies in the line of duty the shockwaves and sadness reverberates throughout the Met and our communities. Policing is a family, within London and nationally, and we will all deeply mourn our colleague.
“We are in the early stages of the investigation and are still working to establish the circumstances surrounding the incident and we will provide further updates when we have them.”
The Met said the incident has been referred to the Independent Office for Police Conduct who will lead an independent investigation.
They said the MPS retain primacy of the murder investigation.
More to follow…