The Telegraph reports that the south bound coach, which belonged to the Megabus company, had already pulled over to the hard shoulder when police arrived at the scene.

A spokeswoman for Megabus, which is operated by Stagecoach, said: "We are assisting police with their inquiries into an allegation made against a passenger who was travelling on board one of our services."

Passengers, many of them appearing to be young adults, were forced to sit on the roadway surface within a police cordon. The incident, which occurred at the height of rush hour, brought chaos to the road network in the area. Fifty people were evacuated from the bus.