A senior civil servant was fined today after pleading guilty to leaving top secret intelligence documents on a commuter train.

Richard Jackson, 37, admitted breaching the Official Secrets Act by failing to by take due care of the documents, which he left on a train at Waterloo station in June.

The highly sensitive files “had the potential to damage national security or the UK’s international relations,” Westminster Magistrates Court heard, but Jackson escaped jail and was instead fined £2,500 because an assessment found the actual damage done had been “negligable”.

The documents were found inside an envelope by a passenger who handed them over to the BBC Security Correspondent, Frank Gardner. He then turned them in to police.

The court heard that one of the documents was marked “top secret”, while the other had a mid-range classification. It is believed that the most secret document was a report about the threat posed by al-Qaeda in Afghanistan and Pakistan. The other is thought to be a highly critical British assessment of the Iraqi security forces.

“My principal concern has been about the degree of harm that may have been caused by this error,” District Judge Timothy Workman said. “Had there been real risks to national security a custodial sentence, possibly suspended, would have been inevitable.”

He added: “I am conscious that he has already paid a heavy penalty, a significant reduction in income and damage to his own and his family’s health”

Jackson, who was on a secondment to the Cabinet Office from the Ministry of Defence, was suspended after the incident. He has since returned to work with a demotion of at least three grades and a “drastic” pay cut.

He was charged under the least serious "safeguarding of information” section of the 1989 Act, which carries a maximum prison sentence of three months. Jackson’s was the first such prosecution since the act was passed.

The court heard that Jackson accidentally took the documents home with him on June 9 after picking them up with some magazines. He realised his mistake on his way home to Yateley in Hampshire and brought the documents back with him the next morning.

When he got off the train at Waterloo, however, he forgot to pick them up from the seat next to him. By the time he realised his mistake the train was on the way to Woking.

Jackson did not report the loss of the documents until the next day, as both his immediate bosses were abroad.

“This delay in reporting delayed any action to recover the files, the prosecution said.

Jackson’s lawyer, Neil Saunders, told the court that his client “accepts that he mas made a terrible mistake” but said “there was never any risk to any lives whatsoever.”

Before the incident Jackson was talked about “in the most glowing of terms”, Mr Saunders said, and “was obviously destined for a notable career in public Service”. The “extreme pressure” he was under at the time may have contributed to the “gross error of judgement”, Mr Saunders claimed.

In court today, Jackson spoke only to confirm his name and plea, spending much of the proceedings with his head in his hands.

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