According to one of the passengers, the aircraft's cabin crew said two men had repeatedly tried to get into the cockpit.
Umari Nauman told Sky News: "The cabin crew informed us that basically they tried to come into the cockpit a few times and because they had been asked not to do that they got into a bit of an argument with the crew and made a few threats."
She said all the passengers had been ordered to leave their possessions on board before leaving the plane.
Ms Nauman also said helicopters escorted the aircraft before landing.
More top news
Clear tonight with temperatures falling quickly. Light winds and lows of 5C.
An elderly and vulnerable man is fighting for his life after being mugged while riding a mobility scooter.
The latest disruption on an increasingly delay-affected Underground system was on the Central line.