One person's been arrested after a string of pepper spray attacks at London's Heathrow Airport.

Twenty-one people suffered injuries, with five needing hospital treatment, after an argument escalated in a terminal carpark. 

Social media footage shows a large armed police response, as the area was temporarily locked down.

UK correspondent Gavin Grey told Andrew Dickens police were quick to say it wasn't related to terrorism or a protest.

He says the people seemed to know each other, and got into an argument, which led to someone spraying a substance at people they didn't like.