Extra police are on duty in London and security has been increased on the first anniversary of the 11 September terrorist attacks.

Hundreds of extra officers have been drafted in from outside the city, or from administrative roles, to police high profile sites like the US Embassy in Grosvenor Square, west London.

Police will also be guarding routes in and out of the City of London.

But while Scotland Yard is on alert it does not believe London is the target of any large-scale terrorist attack.

Police 'pragmatic'

Areas around the US Embassy in Grosvenor Square and St Paul's Cathedral, where remembrance services will take place from 1315 BST, will be closed.

Ministry of Defence and Special Branch officers, who have been guarding the entrances to the embassy, have been criticised by some staff for their relaxed demeanour.

But Chief Inspector Alan King told BBC London: "For the last three decades the British police have worked policing the capital and the rest of the country with the shadow of terrorism hanging over us.

"That has not made us complacent or laid back, we are pragmatic."

Commander Frank Armstrong, from City of London Police, told BBC London that they had policed St Paul's many times and had their contingency plans tested on the Queen's Golden Jubilee.

"The threat from international terrorism is still here but there is no specific intelligence to suggest that London or St Paul's will be the target," he said.