UK armed police arrested a man on Sunday for suspected assault after 21 people needed medical treatment following an incident involving “a form of pepper spray” at a Heathrow Airport car park.

London’s Metropolitan Police said the incident at Terminal 3’s multi-storey car park was sparked by an argument between “a group of people known to each other” and was not being treated as terrorism.

Emergency responders treated 21 patients, with five taken to hospital, the London Ambulance Service said.

Police noted all the injuries were “not believed to be life-changing or life-threatening”.

Heathrow advised passengers to allow extra time when travelling to Europe’s busiest airport.

Terminal 3 remained open throughout but the incident prompted severe traffic and public transport disruption in the area, according to officials and reports.