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

The documents belonged to a senior intelligence official in the Cabinet office and were found by a passenger on a London commuter train Tuesday. The envelope was then passed to the British Broadcasting Corp.

Seven pages stamped "UK Top Secret" included the latest government intelligence assessment on al-Qaida and Iraq's security forces, the BBC said. The documents were also stamped "for UK/US/Canadian and Australian eyes only." The first page was dated June 5, the BBC reported.

Two of the assessments were made by the British government's Joint Intelligence Committee. The report on Iraq was commissioned by the Ministry of Defence. The al-Qaida report was commissioned by the Foreign and the Home Offices.

The assessments often include 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," according to a Cabinet office spokesman who spoke on condition of anonymity in accordance with government policy for civil servants.

The intelligence official was still working at the Cabinet office, pending a police investigation.

Britain's Official Secrets Act prohibits the passing of sensitive information that could affect national security.

The BBC said it could not reveal the documents' exact contents after receiving legal advice.

The security assessments often include intelligence material gathered from agents on the ground and could prompt terror cells to change tactics or alert terrorists to British surveillance techniques, according to a British security official who spoke on condition of anonymity because of the sensitivity of the story.

The security breach is the latest in a string of government data losses and comes as Britain pushes for an expansion of its national DNA database — already the largest per capita in the world — and works to finalize plans for an ID program.

"This is just the latest in a long line of serious breaches of security ... further highlighting the most basic failures in this government's ability to maintain our security," said Pauline Neville-Jones of the opposition Conservative party.

A computer containing sensitive details on 600,000 prospective military recruits was snatched from the car of a Royal Navy recruitment officer in central England in January.

The data included details of candidates' religions and some banking records. It was not encrypted.

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

"There should be strict guidelines about when such secret documents are outside carefully monitored premises," said Chris Huhne with the Liberal Democrats, the third largest opposition party.

Editor: Yan