Detectives investigating a sexual assault on a teenage girl who was walking across a field are appealing to a dog walker who stopped the offender in his tracks to come forward.

The 14-year-old girl was on a field behind Park Road in Westhoughton at about 8.30pm on Saturday.

The offender then approached her from behind, pinned her up against a tree and kissed her on the neck.

He was disturbed by a passing dog walker and ran off. The dog walker asked if she was OK and the victim said yes. She then went to see friends and told them what happened and the police were called.

The offender is described as being white man with short brown hair, in his late 20s to early 30s, of average build. He was wearing blue jeans and a dark top.

Detective Constable Dave Harris said: “This was a terrifying experience for the victim and I suspect that she said that she was OK to the dog walker because she was still in a state of shock.

“This passerby therefore carried on with his business and we have no details of who this is.

“I would urge this man to come forward and speak to the police as he may be a vital witness.

“Specially trained officers are offering support to the victim and we are making thorough inquiries.

“I would like to reassure the community that offences of this nature are rare.”

Anyone with any information is asked to call police on 0161 856 5740 or call the independent charity Crimestoppers anonymously on 0800 555 111.