A teenage gang bludgeoned a policeman with a crow bar and broken bottle after he saw them getting into a stolen car.

Detectives today branded the attack in Denholme as "despicable", saying the youths casually strolled away from the scene as the off-duty bobby lay seriously injured on the ground.

The 47-year-old - who works for the Greater Manchester force - was driving in Trough Lane at about 1.45am yesterday when he saw a group of youths running away from a car which had left the road and ended up in a field.

Police later discovered the red Vauxhall Astra had been stolen from Bradford's Holme Wood estate.

The officer followed the youths - some as young as 13 - for three quarters of a mile to the car park of the Five Flags Hotel in Manywell Brow. When he spotted them getting into a Rover Metro, which had earlier been stolen from Baildon, he called for police back-up and stepped in to confront them.

A police spokesman said the gang became aggressive and turned on the officer with a crow bar and broken bottle. He said the constable, who lives locally, was battered around the head and body, suffering serious cuts and a shoulder wound. As their victim lay injured on the ground, the youths casually walked away from the scene and escaped.

The spokesman said: "A number of vehicles are believed to have passed the group at this time and police are appealing to anyone who saw them to come forward as they may hold vital information about this crime."

The Astra is thought to have been driven around Denholme before the incident and he called on residents who saw it to contact detectives on (01535) 617083.

The police officer was treated at Airedale General Hospital and later released. He was recovering at home today.

The first suspect was described as white, aged between 18 and 20, 5ft 10ins tall with a slim and athletic build. He wore a flat white cap, dark tracksuit bottoms, a dark woolly jumper and a dark grey shirt.

The second was white, slim, about 15 or 16, between 5ft and 5ft 6ins tall, with short dirty-blond hair.

They were with another white male and three white females, aged between 13 and 15 years old. One girl was wearing white trousers.

Acting DCI Trevor Gasson said: "This was a despicable and violent attack." Officers were following a number of leads, he said.