A passenger using an electronic cigarette which gives off a vapour caused armed police to swoop on a coach in a terror alert which closed a motorway for more than four hours.

Armed officers, troops, firefighters and bomb disposal experts all went to the scene on the M6 toll road near Lichfield after a passenger reported seeing vapour coming from a man's bag.

A decontamination unit was set up and passengers were searched and held in a makeshift pen on the carriageway, but police found no crime had been committed. The man was simply using an electronic cigarette, rather than the real thing, on the six-hour journey from Preston to London.

Passengers arriving back at Victoria Coach Station in London on Thursday night spoke of their terror as they thought they would die when armed police swooped on the bus.

Student Vermilion Von Kangur, 20, said: "I was scared. I thought there might have been a bomb on the bus."

She said everyone on board was made to it leave one by one with their hands clearly visible and out of their pockets as officers looked on with their guns poised.

Ms Von Kangur said: "My legs were like jelly, I couldn't walk. I felt very intimidated. I thought if I moved I would get shot."

A Staffordshire Police spokeswoman said: "We can now confirm that, whilst this was a genuine security alert, the significant concerns reported to us were unfounded. It's important to state that no criminal offence has been committed and no passenger or any other member of the public is being treated as a suspect."

Police received a report at about 8.20am on Thursday from "a genuinely concerned member of the public" who saw vapour coming out of the bag as the coach was near the M6 toll plaza at Weeford, near Lichfield. The incident shut the M6 toll road in both directions for more than four hours.

A spokeswoman for Megabus, which is operated by Stagecoach, said 48 passengers were booked on the service and all were safe and well. She said: "Police have confirmed that all passengers are safe and well and they have been transferred to a substitute vehicle."