MINISTERS in Tony Blair’s government were taken aback by the scale of a military operation to secure Heathrow Airport from an al-Qaida attack, newly released official files suggest.

The then prime minister rubber-stamped the decision to deploy about 450 heavily armed troops, some in armoured vehicles, to create a “ring of steel” around Britain’s busiest airport in February 2003 after intelligence identified it as a likely target for an imminent attack by militants armed with anti-aircraft missiles.

Files released by the National Archives at Kew, west London, show that then home secretary David Blunkett told the Cabinet that while the deployment had been agreed with the security services and the military, they had not been expecting such a high-profile show of force.