A serving Hounslow detective could face the sack after chanting obscene football songs on a packed commuter train, it emerged today.

Detective Constable James Coleman, 27, was among a group of rowdy Bristol City fans who yelled offensive songs, which left other passengers intimidated and distressed.

Unfortunately for Coleman, one of the passengers in the same carriage was City of London Police Commissioner Mike Bowron, who was also on his way to the evening match in south-east London.

Mr Bowron produced his police identification, and politely urged them to tone down their foul language, but was subjected to a torrent of further abuse.

At one stage, it has been reported that the 51-year-old commissioner feared he would be physically assaulted by the mob.

However, without revealing his rank, he stood his ground. As he left the train, one of the hooligans quipped that one of his foul-mouthed friends was also a policeman.

Mr Bowron was so incensed by the revelation that he decided he should take further action.

He made a formal complaint to British Transport Police over the incident, which took place before Charlton's home defeat against Bristol City last October.

BTP officers seized CCTV images of the suspects and circulated them to other forces. A special appeal was also made in the Bristol area, where it was thought the policeman might be based.

But it turned out he worked in the capital. A Metropolitan Police officer recognised Coleman - a detective constable in Hounslow.

He contacted BTP, naming his colleague as one of the troublemakers on the 6.34pm Charing Cross to Dartford service on October 21.

Coleman was later charged with disorderly behaviour causing harassment, alarm and distress after being picked out of CCTV footage by Mr Bowron.

Initially, his defence team told Westminster magistrates he had been unfairly prosecuted because he was a police officer, arguing the matter should instead have been dealt with internally by a disciplinary inquiry.

But on legal advice, he changed his plea to guilty last month, ahead of the trial scheduled for May 19. He was handed a £300 fine and ordered to pay £100 costs.

Colleagues of Coleman have reportedly said he was greatly embarrassed by the case. One said: "From what I can gather, he had no idea that the officer on the train was such a high ranking policeman."

Another said: "Mr Bowron should be congratulated for taking a stand against yobs. For too long people have turned a blind eye to rowdy football fans."

Scotland Yard said Coleman was on "restricted duties" pending the outcome of disciplinary proceedings.

Sources said it was "virtually inconceivable" he would keep his job.