Armed police have responded to a major incident at Heathrow Airport in London as several areas have been locked down while witnesses report that someone 'sprayed an unknown gas'

A major incident is unfolding at Heathrow Airport with armed police at the scene and drivers urged not to leave their vehicles at Terminal 3 car parks

Searches continue for more suspects, after armed police arrested a man at a Heathrow Airport car park on suspicion of a "pepper spray assault". A total of 21 people were treated, with five taken to hospital.

The Heathrow Express website warns of 'major disruption', saying there are 'no services in either direction due to a problem currently under investigation'.