A runaway double-decker knocked over two sets of traffic lights and smashed into an office block after its handbrake was deliberately released.

It is alleged vandals set loose the driverless bus, which was parked in Queen's Road, a few yards from Brighton station, last night.

It careered down the hill and into the Lloyds TSB building at the corner of Gloucester Road.

It rolled on to the pavement, knocking over two sets of traffic lights and a signpost, before crashing into the front window of the offices at about 8.25pm.

Police were last night investigating the vandalism allegations.

Nobody was injured but police had to divert traffic around the junction as engineers from Brighton and Hove City Council secured the building and towed the bus away.

Eye witness Tung kwan Lam, of Queen's Road, said: "I saw the bus moving very slowly down the road and I immediately knew something was wrong because none of its lights were on.

"I watched as it gathered speed and careered off the road and into the traffic lights. It was lucky the building was in its way because otherwise it would have got faster and faster as it went down the hill."

Brighton and Hove Bus Company's operations manager Paul Williams said: "It seems an unknown person let off the handbrake while it was stationary.

"The driver was in the vicinity of the vehicle but not inside. There was no one inside. The front of the bus is fairly extensively damaged. It is not a write-off and is now in our garage."

A police spokeswoman said: "It rolled down Queen's Road at approximately 10mph. It collided into two sets of traffic lights before embedding itself in a building 50 yards from where it started.

"Police are investigating why the parked, unattended bus rolled off down a busy street.

"Inquiries are continuing to find out the cause of the accident and anyone who can help should call us on 0845 6070999."