A passenger on the Megabus coach headed from Preston to London raised the alarm after seeing a “vapour” coming from a bag.

Armed police were called to the scene and the bus was evacuated, forcing a large stretch of the M6 near Lichfield in Staffordshire to be closed in both directions.

Sniffer dogs were sent to the scene and the Megabus passengers were searched on the roadside as the area was cordoned off.

But police have now concluded that the terror scare was down to a “health improvement aid for smokers” that was emitting a “vapour” from a passenger’s bag.

A Staffordshire Police spokeswoman said: “Given the credibility of the information we received, we responded swiftly and proportionately. We can now confirm that, whilst this was a genuine security alert, the significant concerns reported to us were unfounded.”

She added: “The information received concerned a report of vapour escaping from a bag which on investigation turned out to be a health improvement aid for smokers.

“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.

 “We would like to apologise for any inconvenience and hope that the public understand that we have our duty to safeguard public safety.”

Police launched their response after receiving a call from a passenger at 8.20am. Officers closed the motorway at the height of rush hour, stranding scores of motorists.

Image: Getty