Investigators are examining CCTV footage in a bid to establish why a double-decker bus went out of control, ploughed into railings and parked cars, and left the driver impaled by a metal spike.

Police and First Bus experts are working on the possible theory that another vehicle may have caused the bus to swerve, leading to the crash.

The 23-year-old driver, who was trapped in his vehicle for an hour and a half with the rod through his leg, is likely to be in hospital for several weeks and face a series of operations.

The accident happened just after midday on Boxing Day as the 363 Huddersfield to Bradford service, with 25 passengers on board, was being driven down Manchester Road towards Bradford city centre.

The bus suddenly veered into the central reservation barrier, leaving a large hole, then hit at least five parked or stationary cars on the nearside, outside a row of shops.

The metal handrail from the barrier pierced the front of the bus, entered the front of the driver’s leg, exited through the back of his leg before skewering the back of his seat, pinning him in his cab.

Passengers were led from the bus by a rear emergency door while the delicate operation to rescue the driver began.

A dozen passengers suffered minor injuries, including whiplash and shock. Many were taken into local shops and comforted, while two were taken to hospital by ambulance.

The driver was eventually airlifted to Leeds General Infirmary, after firefighters used a special saw to cut off the ends of the rod.

A spokesman for First Bus said yesterday that the driver, who is from Huddersfield, had undergone surgery, which included the removal of the rest of the spike.

The spokesman said: “As part of his recovery, he is expected to have more surgery. The condition of the driver remains serious, but is not life-threatening. He is conscious. We don’t know when he is likely to be released, but it may be several weeks.”

He said the situation could have been life-threatening without the speed and efficiency of the emergency services.

He said: “We are working closely with police and will be looking at CCTV. We have to speak to witnesses and people on the bus, and at some point the driver will make a statement.

“We are looking at the possibility that a third party vehicle was involved in the incident.”

Any witnesses to the accident are asked to contact PC Michael Wroe, of the Western Roads Policing Unit, on 101.