A woman detective collapsed and died while chasing two suspected phone thieves.
Detective Constable Adele Cashman, 30, who was based in Kentish Town, north London, collapsed about 15 minutes into the chase in Hampstead on Monday evening. She was pronounced dead at the Royal Free Hospital.
Two 17-year-old boys were later arrested and a phone was recovered, Scotland Yard said.
The Metropolitan Police Commissioner, Bernard Hogan-Howe, said her death was a "terrible loss".