Katsutoshi Jitsukawa, a Japan Airlines pilot had almost 10 times more than the legal permitted amount of alcohol in his bloodstream when he was arrested, CNN quoted the Metropolitan Police on Thursday.
The pilot has admitted to failing a breath test shortly before he was due to fly from London to Tokyo, the police said.
42-year-old Katsutoshi Jitsukawa pleaded guilty to the offence at the Uxbridge Magistrates' Court, CNN reported citing UK Press Association reports.
Japan Airlines flight JL44 was due to take off just 50 minutes after tests showed that First Officer Jitsukawa had 189 mg of alcohol per 100 ml of blood in his body.
The legal limit for pilots is 20 mg, while drivers in England, Wales and Northern Ireland are allowed as much as 80 mg.
He was caught after the driver of a crew bus smelled alcohol and called the police, according to Japanese broadcaster NHK.
The pilot was due to fly a Boeing 777 aircraft, which can accommodate 244 flyers. He is currently in custody and will be sentenced on November 29 at the Isleworth Crown Court.
Japan Airlines has apologised for the incident, saying that "safety remains our utmost priority" and it will "implement immediate actions to prevent any future occurrence".
After over an hour's delay, the flight departed under the charge of the two remaining pilots.
(With Agency Inputs)