Police drop one of the three investigations into alleged sex abuse by Sir Cliff Richard

A friend of the singer told the Sunday Times that police are struggling to find evidence to back up the allegations

Cliff Richard leaves the church after the funeral of Cilla Black (AFP/Getty)

Police have dropped one of the three investigations into claims of sexual abuse by pop star Sir Cliff Richard, according to a friend.

As reported by The Sunday Times, the investigation been closed as police are struggling to find evidence to back up the claims.

The paper has reported that Richard's friend, who asked not to be named, said that the singer had given police evidence that he was never alone with two men who claim that he attacked them, in incidents that are said to have occurred in the 1980s.

South Yorkshire Police, the force that is leading the investigation, told The Guardian they would not provide a "running commentary" on the case.

There was similarly no response to the claims from Richard, who is currently preparing for a UK-wide tour that will coincide with his 75th birthday.

Richard will play 29 concerts during the tour, beginning on 29 September in Birmingham and ending at London's Royal Albert Hall on 13 October.

Richard, who has not been arrested or charged for the alleged crimes, has described the allegations as "completely false" and "absurd and untrue" in the past.

Last year, South Yorkshire Police tipped the BBC off that they would conduct a raid on Richard's home.

The BBC covered the raid live with cameras and helicopters, in a piece which Richard's legal team described as "extremely damaging".