A woman in her 20s was allegedly sexually assaulted in an alleyway off The Parade in Watford, police say.

Officers are appealing for witnesses and information following the incident sometime between 3.30am and 5am on the morning of Sunday, April 5.

The suspect is described as a white man aged in his mid-20s, who was of a slim build and around 5ft 5ins tall.

He had short brown hair and was clean shaven was wearing a beige jacket, dark blue jeans, black belt with a silver square buckle.

Detective Constable Louise Cleary said: "It is believed another man came into the alleyway at some point and I would be keen to hear from this person as, whilst you may not have realised this incident was taking place, you may have information which could assist the investigation.

"Whilst it was the early hours of the morning there is a taxi company close by and there could have been a number of other people around who could also assist our investigation.

"If you were in the area that morning and can help please call me."

Anyone with information should contact the Herts Police non-emergency number 101 quoting crime reference number C1/15/1546. Alternatively, call Crimestoppers anonymously on 0800 555 111.