South Yorkshire Police's Chief Constable has revealed officers are in "regular contact" with Sir Cliff's lawyers over allegations of historical sexual assault.
In a letter to MP Keith Vaz, chairman of the Commons Home Affairs Select Committee, Ch Cons David Crompton said the official investigation into the claims had "increased significantly in size".
South Yorkshire Police has declined to comment on the contents of the letter.
It comes after an independent report criticised an agreement between the force and the BBC which resulted in a raid on the veteran pop star's home being broadcast live on television, saying it "interfered with his privacy" and "may well have caused unnecessary distress".
Sir Cliff has not been arrested or charged with any offence.
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