A man has been arrested on suspicion of murder after a policeman died on duty in north London.
The police officer collapsed outside the address after the address
Pc Chris Roberts, 47, collapsed on the pavement shortly after he helped arrest a man at a domestic incident in Brinkburn Gardens, Edgware.
The father-of-three was part of a team of officers called to the address at about 1745 GMT on Boxing Day.
A post-mortem examination will be carried out on Mr Roberts later to establish the cause of death.
The man arrested is in his 30s.
Mr Roberts had been in the Metropolitan Police since 1983.
Metropolitan Police Commissioner Sir Ian Blair said: "I am deeply saddened by the death of one of my officers - a father of three - while on duty, and my thoughts go out to his family, friends and colleagues, especially at this time of year."
Home Office minister Tony McNulty said: "Events such as this highlight the dangers that our police officers face every day when protecting the public."
The Association of Chief Police Officers also offered its condolences.
Two other police officers have died on duty this year.
On 6 May Pc Richard Gray was shot by a man after attending a domestic incident in Shrewsbury. The man then committed suicide by shooting himself.
In June 36-year-old Pc Jonathan Charles Henry was fatally stabbed in Luton. A man is awaiting trial accused of his murder.