One of Britain's top intelligence officials left a file with secret documents about Iraq and al-Qaeda on a train, in an embarrassing government security breach.
A passenger found the orange folder on a train and handed it in to the BBC, which said it contained top secret documents on the 'War on Terror' which should not have been removed from government offices.
The Cabinet Office, the central government department that supports the work of Prime Minister Gordon Brown, acknowledged the incident and said it had called in police to investigate.
“The documents were secret. They were in the possession of a senior intelligence official who works in the Cabinet Office. They were lost on a train,” a spokesman said on Wednesday.
“When the official realised what had happened, he reported it immediately to the Cabinet Office. We called the police in and they launched an investigation.”
A police spokeswoman confirmed that the counter-terrorism command of London's police force was carrying out the probe.
Papers marked 'top secret'
The Cabinet Office declined to comment on the contents of the missing file. But the BBC said they contained two reports, one on Iraq's security forces and one on al-Qaeda.
BBC Security Correspondent Frank Gardner at one point waved what he said were the documents on air. In a subsequent report he said that he had turned them over to police officers.
He said the passenger who found the documents had given them to a local BBC office, which phoned him to have a look.
“As soon as I saw 'UK Top Secret', I thought: 'Wow. This is important'. It reveals what the government knows about al-Qaeda's capabilities, and more importantly, its vulnerabilities.”
The file also contained a 'top secret' and in some places “damning” assessment of Iraq's security forces, Mr Gardner said.
'Lax security' allegations
Government sources suggested that the leak was embarrassing but would not actually hurt Britain's security.
But the news will hurt Mr Brown, who has already been stung by accusations of lax security after a civil servant lost computer disks 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.
Mr Brown, whose popularity has plunged since he took over from Tony Blair last year, is promoting plans to roll out a national identity card system, and opponents of the measure often cite the government's poor record of keeping data secure.
The prime minister won a narrow victory in parliament on Wednesday to extend the period that terrorism suspects can be held without charge.