A police officer was driving "erratically" when he ploughed into a couple as they crossed a busy main road, a court heard.

PC Scott Kerr, of Tayside Police, is accused of driving his silver Audi A3 Quattro at speed from a set of traffic lights in Dundee's Earl Gray Place before colliding with Roderick and Shirley Emslie.

Mr and Mrs Emslie earlier told the court they were half way across the city's Riverside Drive when they heard "squealing" tyres and saw the off-duty cop's car driving "erratically" towards them.

They said Mr Emslie was thrown up in the air, knocking him unconscious, ripping off part of his ear and leaving him with a fractured skull and broken nose.

Mrs Emslie told how skin was ripped off her leg, and that she now has pins holding together bones in her foot.

On Tuesday witnesses to the crash told Dundee Sheriff Court how Kerr had sped away from a set of traffic lights seconds before colliding with the couple.

Simon Mortlock, 55, said he had been sitting at the lights when Kerr, a Tayside Police officer, sped up beside him and "braked severely" to stop.

He said: "It just shot off straight away and accelerated quite severely. By the time I moved half a car length the other car was quite a considerable distance ahead of me.

"I could see the two people crossing the road ahead of me. Everything seemed to be in slow motion. The man was thrown up in the air on impact and she was brushed to the side."

Kenneth Pottinger, 62, told the court that he had just come out of Dundee's railway station and was waiting for a lift when he heard Kerr speed off from the traffic lights.

He said: "I heard the sound of a powerful engine at maximum acceleration heading away from the lights. I saw the car take off at a rate of knots.

"He wasn't even looking out of the front - he was looking over towards me. He looked like he was showboating."

Kerr, 40, of Dundee, denies a charge of careless driving in July 2011.

The trial, before Sheriff George Way, continues.