A dog walker may hold the key to tracking down a sex attacker, police believe.

Officers believe a dog walker may have seen the man following the teenage girl prior to the attack on a footpath between Wells Road and Castle Road, in Epsom, on Tuesday, July 15, at 3.25pm.

The dog walker they want to speak to is short and elderly, with white hair, and was walking a small black and white dog.

The man being hunted by police was Asian, in his mid-30s, with short black hair, and medium to well-built.  He was wearing a black or navy jacket and had stubble or a beard.  It is believed he was on foot.

Detective Constable Tom Gilbert said: "We would ask anyone who has walked their dog in that area in the last few weeks to cast their minds back and think if they were in that location at that time.

"It might be that you didn't see the incident, but saw the man before or after the incident, in which case we would like to hear from you.

"I would like to reassure the community that we are taking this incident extremely seriously and doing all we can to find whoever is responsible."

Anyone with information should call the police on 101, quoting reference P14204524, or Crimestoppers anonymously on 0800 555 111.