The senior intelligence official who left top-secret documents on a train was not authorised to take them out of Whitehall let alone read them on his way home.

Ed Miliband, the Cabinet Office Minister, admitted that there had been “a clear breach of security” when he announced that Sir David Omand, the former Permanent Secretary for Intelligence and Security, would lead an investigation into the case.

The incident comes only weeks before Sir Gus O’Donnell, the Cabinet Secretary, was due to publish his report on improving data security in Whitehall after discs with child benefit records were lost in the post.

The 37-year-old Ministry of Defence official, who has been suspended pending a police investigation, had been seconded to the Cabinet Office for intelligence work. Soon after 6pm yesterday he was taken from his Hampshire house by senior government officials after being identified as the man who lost documents about al-Qaeda and Iraqi security forces.

Although The Times knows his identity the name is not being published after advice from Whitehall that it would place him in danger from terrorists.

The civil servant, who had the highest security clearance, provided analysed reports for the Joint Intelligence Committee using information provided by MI6, the Government Communications Headquarters in Cheltenham and foreign intelligence services.

There were some suggestions in Whitehall that the official, who is understood to earn about £70,000 a year, had written the reports. But the Cabinet Office denied suggestions by the MP Andrew Mackinlay in the Commons that he was a member of MI5.

One of the documents is a seven-page report by the Joint Intelligence Committee on “al-Qaeda vulnerabilities” and referred to assessments of the terrorist organisation in Afghanistan and Pakistan. It was considered so sensitive that each page was marked “For UK, US, Canadian and Australian eyes only”.

The Metropolitan Police has started an inquiry into the circumstances surrounding the loss of the documents, which were left in an orange folder on a train from Waterloo to Surrey on Tuesday. They were handed to the BBC, which returned them to the Government on Wednesday.

Mr Miliband reassured the Commons that there was no evidence national security interests had been damaged or that any individuals or operations were at risk.

He told MPs that the rules about how confidential documents should be removed from Whitehall had not been followed. Documents can be taken on public transport but they have to be kept inside a locked briefcase with two straps at all times. The key should be carried in the owner’s pocket and the case must be held. On no account should the papers be read while in transit in case they are seen by other passengers or left behind.

“This was a clear breach of wellestablished security rules which forbid the removal of documents of this kind outside secure government premises,” Mr Miliband told MPs. In this case “no authorisation was sought”.

Francis Maude, the Shadow Cabinet Office Minister, said: “There can be few greater risks than the casual abandonment of top-secret intelligence material on a train.”

Times Recommends

• Oh no, Mr Darling: you have failed
• BBC survives dogfight over Kennel Club expose
• Where the Rosetta belongs can’t be set in stone