Liberal Democrat president Tim Farron says his party needs to answer "serious questions" about who knew that its former MP, Sir Cyril Smith, faced allegations of sexual assault.
Police are investigating allegations that the former MP for Rochdale, who died in 2010 aged 82, sexually abused boys at homes and hostels in the town.
Mr Farron said the police inquiry was the best way to deal with the claims.
The Crown Prosecution Service has said Sir Cyril should have been prosecuted.
It has been alleged Sir Cyril raped boys at Rochdale's Knowl View residential school, which closed in 1992, and abused boys at the privately-run Cambridge House children's care home, which closed in 1965.
Sir Cyril was originally a Labour councillor in Rochdale and later a Liberal then Liberal Democrat MP for the town from 1972 to 1992.
Mr Farron said: "The party absolutely, as the Labour Party must also... and indeed Rochdale civic society as a whole, need to answer serious questions as to who knew what and when."
Lord Steel, who led the Liberal Party between 1976 and 1988, has said he will co-operate with any police inquiry.
"I agree that there should be a fresh inquiry and am happy to be interviewed, having known nothing beyond the 1979 published report of police investigations when Cyril Smith was a Labour councillor in the Sixties," he told the Daily Telegraph.