The police watchdog has launched an investigation into the death of a man who died the day after being arrested.
The 26-year-old was detained on Brandon Street in Southwark, south London, at about 11:30 BST on Friday.
An ambulance was called shortly after he arrived in custody as officers believed he had “swallowed something”, but he died in hospital on Saturday.
The Met Police said it had referred itself to the Independent Office for Police Conduct (IOPC).
The man was in a car which was stopped by officers when he was arrested on suspicion of being in possession of a knife, the force added.
IOPC regional director Sarah Green described the death was “tragic” and said investigators had already been to Walworth Police Station to carry out “post-incident procedures”.
She added: “We were made aware of the man’s arrest, and that he had been taken to hospital, on the afternoon of 30 March.
“We will be offering the man’s family regular updates on the progress of our investigation.”
The Met Police said a post-mortem examination will be held in due course.
A spokesman added: “A lock knife was found in the car and the man was arrested.
“The Met’s Directorate of Professional Standards is investigating and a referral was made to the Independent Office for Police Conduct who have begun an independent investigation.”