Onlookers watched in amazement as a driverless car "drove off" of its own accord, did a U-turn and smashed into a shop window.

The empty vehicle set off from its parking spot by the side of a busy road, rolled downhill in an arc across two lanes, mounted the pavement and crashed into a furniture store.

Staff at the shop, P.H. Buxton and Son in Ditchling Road, Brighton, couldn't believe their eyes as the car hurtled towards their front window shorlty before 3pm yesterday.

The impact smashed the window glass but no one was injured.

Buxton's sales assistant Ali Saddighzadeh said: "I thought someone was going to do a U-turn, which was a surprise because it's a one-way street, and then I just heard the bang.

"I looked up and it was a shock when I realised there was no one in the car.

"It's lucky no one was walking past at the time. I was with a customer, and the lady had a fright when the car hit the window."

Buxton's director Paul Summers said he had noticed the car earlier because it was parked flush up to the bumper of a car in front.

He said: "When the car in front pulled away and drove off, it just began to roll, came right across the road and, 'biff'."

The car's owner, pensioner James Hewitt, 69, of St James's Avenue, Brighton, had parked the car and gone to the supermarket. On his return, he said: "I had a bit of a shock when I saw the car. I had left it parked on the other side, I don't know what happened."

Police were investigating if the handbrake had failed or if it had been left off.