London: The government on Thursday said  it would hold an inquiry into how a senior intelligence official left a file with top secret documents about Iraq and Al Qaida on a train.

A passenger found the orange folder on a London commuter service and handed it over to the BBC, which said it contained highly sensitive details about Iraq's security forces and the government's latest assessment of Al Qaida.

The papers had been with an unnamed official who worked in the Cabinet Office, the central government department that supports the work of Prime Minister Gordon Brown. The official has now been suspended from his duties.

Brown said it was "a very serious incident" and that an inquiry would be held.

"We will have to trace where these documents have gone, if they have gone anywhere other than in an envelope to a local BBC station," he told reporters. "We will inquire and report on all the circumstances in which this happened."

Government sources indicated the news was more embarrassing than a threat to Britain's security.

But the revelation is another blow for Brown, who has already been stung by accusations of lax security after a civil servant lost computer discs containing the names, addresses and bank details of 25 million people in the mail last year.

In January, the Ministry of Defence reported it had lost a laptop containing personal data on 600,000 recruits.

Opponents to Brown's plans for a national identity card system cite the government's poor record of keeping data secure. The Conservatives said the latest incident highlighted "basic failures" in the government's ability to maintain security. "This is just the latest in a long line of serious breaches of security involving either the loss of data, documents or government laptops," said the party's security spokesman, Baroness Pauline Neville-Jones.