Intruder gets into Downing Street grounds with knife

An intruder with a knife has been arrested inside the high-security grounds of British Prime Minister Tony Blair's Downing Street residence.

But there was no danger to the prime minister or his family, Scotland Yard said, adding that there was a brief scuffle with a policeman after the man scaled a fence behind the building late on Sunday.

The BBC reports the man has been questioned at a central London police station, and a review has been immediately launched into security measures around the Prime Minister.

The man was understood to have climbed over the fence at the rear of Downing Street in Horseguards Parade.

He was then challenged by a police officer and lunged at at a member of the diplomatic protection force who challenged him.

There was a brief struggle, during which the intruder did not use the knife, before he was pinned to the ground, as other officers arrived, at about 10:35pm local time on Sunday (Monday 7:35am AEST).

The police spokesman said the intruder was found to be in possession of a large kitchen knife, and was held on suspicion of affray and assaulting a police officer.

Scotland Yard's counter-terrorism unit has been informed of the incident, but is not currently handling the investigation.

The most serious security breach on Downing Street was in February 1991 when the Irish Republican Army (IRA) launched a mortar shell into the back garden after parking a van in nearly Whitehall.

The mortar exploded, blowing out windows at the back of the building, while then prime minister John Major was conducting a cabinet meeting inside.

- AFP