Erwin Washington, 51, of Lakewood, Colorado, had been due to captain a Boeing 767 bound for Chicago last November with 124 passengers and 11 crew members when a colleague smelled alcohol on his breath.

The flight was "imminent" when police arrived and arrested him. A breath test recorded a reading of 31 micrograms of alcohol per 100 milliliters of breath. The legal limit is nine micrograms.

When arrested Washington, who has a military background, replied: "Okay, fine."

He pleaded guilty at London's Uxbridge Magistrates' Court on Tuesday to being above the alcohol limit for flying a plane, the Press Association reported. His lawyer Chris Humphreys said the pilot was "remorseful."

Humphreys told the court that legislation relating to airline staff over the legal alcohol limit for flying had only been used seven times. "There are, thankfully, very few cases of this sort," he said.

Washington will be sentenced on February 5 and was released on unconditional bail.

United Airlines said he had been suspended pending a full investigation.