Secret government documents on Al Qaeda and Iraq were left on a commuter train, prompting a major police investigation into the latest in a series of high-level security breaches, British officials said Wednesday.

A passenger found the envelope on an empty seat aboard a London commuter train Tuesday. The documents were then given to the British Broadcasting Corp., the broadcaster said.

Seven pages stamped "UK Top Secret" included the latest government intelligence assessment on Al Qaeda and Iraq's security forces, the BBC said. The documents were also stamped "for UK/US/Canadian and Australian eyes only."

Two of the assessments were made by the British government's Joint Intelligence Committee. The report on Iraq was commissioned by the Ministry of Defense. The Al Qaeda report was commissioned by the Foreign and the Home Offices. Some of the assessments came from intelligence material gathered from agents on the ground.

"Two documents which are marked as secret were left on a train and have subsequently been handed to the BBC," said a Cabinet spokesman, who spoke on condition of anonymity in accordance with government policy for civil servants.

The documents were in the possession of a senior intelligence official, he said, adding that government policy required such secret documents to be safeguarded.

Intelligence officers — including representatives from MI6 — regularly attend Cabinet meetings. The government, however, would not provide any information on the intelligence officer.

The security breach is the latest in a string of government data losses.

Earlier this year, a computer containing sensitive details on 600,000 prospective military recruits was snatched from the car of a Royal Navy recruitment officer in Birmingham, central England. The data included details of candidates' religions and some banking records. It was not encrypted.

Last year, tax officials lost computer disks containing information — including banking records — on nearly half the British population.