A US air marshal, who was armed with his service weapon, reportedly was removed from a passenger jet at London's Heathrow Airport because he was allegedly intoxicated.

Metropolitan police officers were called to a Los Angeles-bound plane at Terminal 2 after the United Airlines captain claimed a man was trying to board under the influence of alcohol.

A police spokesman said the man was breathalysed and arrested, but released from custody a short time later with no further action.

Police were called after the captain suspected a passenger was under the influence of alcohol (file photo)

When police were called to the plane they were told the man ‘stank of booze’ as he arrived for the long-haul flight, according to a report in The Sun.

He was hauled off the Boeing 777-200, which took off two hours behind schedule, leaving passengers upset, and taken to Heathrow’s police station.

Flight 935 was carrying up to 269 passengers on the transatlantic flight last Monday.

A source on the plane told The Sun: ‘The captain smelt alcohol on the breath of one of four armed US air marshals who were on board.

‘Police were called. It caused quite a scene.’

Flight 935 was carrying up to 269 passengers on the transatlantic flight from Heathrow's Terminal 2

The Federal Air Marshal Service is part of the Transportation Security Administration and has a motto of ‘detect, deter, defeat’.

The TSA confirmed to MailOnline Travel that it is aware of an alleged incident involving an employee.

A spokesperson said: 'While we cannot comment publicly on internal matters currently under investigation, we take all allegations of misconduct seriously.

'TSA holds its employees to the highest ethical and professional standards of conduct and takes appropriate action when allegations of misconduct are substantiated.'

Air marshals are not allowed to consume any alcohol within four hours of a non-mission flight and eight hours of a mission flight.

A Scotland Yard spokesman told MailOnline: ‘On Monday, 9 May police were called at around 12:25pm following concerns by the captain of a flight due to leave Heathrow for Los Angeles that a person trying to board was under the influence of alcohol.

‘Officers attended and breathalysed a man, and he was subsequently arrested on suspicion of being over the prescribed limit.

‘The man was taken into custody at Heathrow Police Station but released shortly after with no further action.’

A police source told The Sun the man had not broken any UK laws.