The former PM, who was reportedly travelling with his wife, Samantha, on the BA flight from New York to Heathrow, is entitled to ongoing protection from armed officers.

But the weapon, believed to be a 9mm Glock 17 pistol, was found by a "terrified passenger" after one of Mr Cameron's bodyguards is said to have removed his holster while in the stall.

The man quickly handed the weapon to flight crew who informed the pilot, according to the Daily Mail [1], before the gun was eventually removed from the plane after passengers reacted with anger to the incident.

One traveller told the Sun: "We were waiting for take off when a guy started to show pictures on his phone of a gun and two passports - one was David Cameron's - he said he found in the toilet.

"They were just resting on the side by the sink. He was stunned by what he saw."

Another businessman travelling on the flight, said: "There was a real commotion going on with a guy near to me. He said he had found a gun in the toilets, which was met with disbelief.

"A few minutes later the captain came into our section and confirmed a gun had been found - which freaked everyone out.

"He tried to calm everyone down by explaining that the law allowed handguns on planes for protection officers and that the gun was back with the bodyguard.

"But a guy wasn't having it. He said he felt uncomfortable about guns being allowed on the plan.

"The captain left and came back a few minutes later to say the gun had been removed from the plane."

A spokesperson for the Metropolitan police confirmed the officer had been suspended following the incident.

"We are aware of the incident on a flight into the UK on February 3 and the officer involved has since been removed from operational duties.

"We are taking this matter extremely seriously and an internal investigation is taking place."

In 2012, Mr Cameron's security detail faced criticism after it was revealed the then-Prime Minister had left his eight-year-old daughter in a pub following a mix-up with travel arrangements.

Nancy Cameron was quickly collected by her mother after the mistake was noticed 15 minutes later, and no close protection officers faced disciplinary action.