Detectives are appealing for witnesses to a serious collision in Bromley.
Police were called at 13:44hrs on Monday, 20 February, to reports of a moped in collision with a male pedestrian in Beckenham Road, Bromley opposite Clock House railway station.
London Ambulance Service also attended and took the pedestrian, aged in his 70s, to a south London hospital. His condition is critical.
The 21-year-old rider of the moped stopped at the scene. He was arrested and taken to a south London police station, where he remains in custody.
Detectives from the Serious Collision Investigation Unit based at Catford are investigating.
Anyone who witnessed the collision is asked to call police on 020 8285 1574.