A police officer has been shot dead while trying to detain a man at Croydon Police Station in south London.The officer was shot by the 23-year-old in the early hours of Friday morning.In a statement, Scotland Yard said: "At approximately 0215 on Friday, September 25 the officer was shot by a man who was being detained at Croydon Custody Centre in Windmill Lane."Officers and paramedics treated him at the scene and he was taken to hospital by London Ambulance Service.