400 troops guard Heathrow Airport

More than 400 soldiers have been drafted in to provide extra security at Heathrow Airport to combat terrorist threats to London.

Troops took up their new positions at one of the world's busiest international airports at 6am on Tuesday as part of a "precautionary measure" linked to fears that al Qaida could use the end of the Muslim festival of Eid, which runs from Wednesday until Saturday, as a trigger for attacks.

The strengthening of security in London will continue "for as long as the Metropolitan Police requires our assistance", said a spokesman for the Ministry of Defence.

In a statement, the Yard said its decision to call in the troops - from the First Battalion Grenadier Guards and the Household Cavalry Regiment - was a "necessary" and "prudent" step to take in the light of international activity.

It read: "From time to time, it is necessary to raise levels of security activity.

"We think it is prudent to do so now. The current strengthening of security is precautionary and is related to action being taken in other countries and the possibility that the end of the religious festival of Eid may erroneously be used by al Qaida and associated networks to mount attacks."

Strengthened security would be most visible at Heathrow but other sites would be on higher alert.

"The use of troops is part of a long-standing contingency, authorised by the Government, for example during the Provisional IRA campaign.

"To avoid prejudicing ongoing operations, we do not intend to give any further details of security arrangements, other than to say that this action is in line with the policy of taking whatever action we believe necessary to protect the public."

In November, a statement authorised by Home Secretary David Blunkett warned of "ever more dramatic and devastating" terror attacks, but avoided mention of the specific threats.

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