Members of the public are thought to have broken up an alleged sexual assault on Richmond bridge after they heard a woman screaming.

Detectives said they were told about the alleged attack, said to have happened on Thursday, November 5 at about 11.30pm, by a member of the public but that the woman involved had not contacted them.

A witness said they saw a man lying on top of the woman with his trousers around his ankles on the Twickenham side of the bridge.

The man walked off towards Richmond Road, police said, and the woman followed him, shouting. Neither has been identified.

Detective Constable Leo Farnon, from Richmond police, said: "We take any allegations of this nature very seriously and investigate them accordingly. However, we do keep an open mind regarding any incident. 

"It may be that there is a reasonable explanation to account for what someone thinks they witnessed, but we are always thankful for vigilance shown by the public when they report anything suspicious.

"However, we are concerned that potentially there could be a victim of a crime that hasn't been identified, and we would appeal to this person to contact us."

Anyone with information should call police on 020 8721 5898, or Crimestoppers anonymously on 0800 555 111.