A Metropolitan Police officer who suffered serious head injuries while investigating a robbery has died.
Armed officers attempted to stop a vehicle in Stratford, east London, early on Saturday morning.
They followed the car to Ashlin Road in Newham, where 37-year-old PC Gary Toms was critically injured.
Pc Toms, who joined the force in January 2002, has been described as a "dedicated officer" who was known for his "professional attitude".
The officer's death comes on the day the Met marked the 25th anniversary of the death of Pc Yvonne Fletcher who was shot dead while policing a demonstration outside the Libyan Embassy in 1984.
Commissioner Sir Paul Stephenson said: "It shows us all that the potential dangers officers face when doing their duty are never far away.
"To lose such a young and promising officer is the most tragic of losses for his family - my most sincere condolences to them.
"This is also a loss that the wider Met family should not, and never will, forget."
Ch Supt Bill Tillbrook, head of the Met's Specialist Firearms Command, said: "Gary was a dedicated officer who died doing the job he had trained to do.
"He was a hard working police officer who was known amongst his colleagues for his sense of humour and professional attitude."
The force said it is investigating the exact circumstances that led to Pc Toms' fatal injuries.
A fourth person has been charged with robbery following the incident in Dagenham.
Austin Ante-Taylor, 19, of Oak Lodge Avenue in Chigwell, is due to appear before Waltham Forest Magistrates' Court on Saturday.
Mansour-Jacques Jallow, 26, Temitope Iyiola, 19, and Mary Fowler, 21, had previously been charged with robbery and have been remanded in custody.
Mr Jallow and Miss Iyiola, both of no fixed address, and Miss Fowler, of Ibex House, Forest Lane, appeared at Waltham Forest Magistrates' Court on Thursday.