A woman, who was sexually assaulted by a man claiming to be a taxi driver, had been at the Derby earlier that day, it has emerged.

The attacker pushed the victim in her 20s to the ground and sexually assaulted her in the street on her way from a party in Tadworth to Tattenham Corner.

She broke free and fled to the station where a man, standing at a bus stop in Great Tattenhams, helped her onto a train home to Purley at about 10pm.

Police, who are trying to locate exactly where she was attacked, are carrying out house to house enquiries in the area.

A police spokeswoman said a medical examination has been carried out.

She said: "Victim care is paramount. She had been at the Derby but the assault was not connected in any way.

"Our understanding is it was completely unrelated."

The attacker, who was on foot, offered a lift to the woman but she refused and he sexually assaulted her sometime between 9.15pm and 9.50pm.

He was black, with short hair and muscular build, spoke with a South London accent and was wearing a white t-shirt with a collar and dark trousers.

Detective Sergeant Mark Parry appealed for witnesses and anyone with information to come forward.

He said: "This report is very concerning and we are working to piece together any information that could help to identify this man.

"I particularly want to speak to the person who assisted this distressed woman in getting on a train at Tattenham Corner Station."

He added: "The victim is currently being assisted by specialist officers and we will fully support her throughout this investigation."

The victim lost two gold bangles during the sexual assault and police have asked for these to be handed in if found.

Reigate and Banstead Neighbourhood Inspector Richard Haycock said: "I would like to reassure local residents that incidents of this nature are extremely rare in this area and officers are doing everything they can to piece together what has taken place and identify and trace the offender responsible."

Anyone with information should call Surrey Police on 101, quoting reference RB/13/4294, or Crimestoppers anonymously on 0800 555 111.