A police car flipped upside down after it collided with a moped suspected in a "series of offences" near Buckingham Palace.
Officers spotted the moped at 4.30am began to pursue it as "the vehicle, rider and pillion passenger matched the description of a moped believed to have been involved in a series of offences".
The moped then collided with a second police car travelling in the opposite direction in Grosvenor Place, outside the palace's grounds.
A 17-year-old boy was taken to hospital with serious injuries following the incident.
He was later arrested on suspicion of a number of motoring offences.
Police say they are still looking for a second suspect who fled the scene.
The collision is now being investigated by the Independent Office for Police Conduct (IOPC).
A spokesperson for the IOPC said: "An independent investigation has been launched following a collision between a moped and a marked police car in Westminster, London, this morning.
"A 17-year old boy has suffered serious leg injuries and been taken to hospital.
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"A police vehicle overturned during the incident but no police officers have sustained injuries."