The former Prime Minister Sir Edward Heath has been accused of raping a 12-year-old boy in a Mayfair flat in 1961.
A man has claimed he was sexually attacked by the politician in 1961 - as police urged other potential victims to come forward.
The alleged victim, now aged in his 60s, claims he was branded "a liar and a fantasist" when he initially reported the alleged assault in the 1960s.
The Daily Mirror has reported that the man said Sir Edward picked him up along the A2 road in north Kent as he hitched a lift.
He claimed to have gone back to an apartment in Park Lane, London, where he was raped, the newspaper reported.
It was not until 1965 that he realised who his alleged abuser was, recognising him from a picture in a newspaper, standing beside Margaret Thatcher.
"I learned that he was MP for Bexley," he said in statements to his legal team reported in the newspaper.
"This answered a lot of questions as to why no-one believed me about the London saga. I got called a liar and a fantasist."
The Metropolitan Police declined to comment on the claims.
Sir Edward, who was PM for four years in the 1970s, is the highest-profile figure to be named in historic abuse allegations against prominent figures.
The allegation comes after the police watchdog said it was looking into whether Wiltshire Police followed up claims against Sir Edward, made in the 1990s.
An IPCC spokesman said: "It is alleged that a criminal prosecution was not pursued when a person threatened to expose that Sir Edward Heath may have been involved in offences concerning children.
"In addition to this allegation, the IPCC will examine whether Wiltshire Police subsequently took any steps to investigate these claims."
Wiltshire Police have appealed for potential victims of Sir Edward to come forward.
Superintendent Sean Memory of Wiltshire Police said: "The allegation is that a trial was due to take place in the 1990s and information was received in that trial that Sir Ted Heath was involved in the abuse of children and the allegation is from the result of that information that the trial never took place.
"A retired senior police officer has come forward towards the end of 2014 indicating that they were aware of this information.
"This is an appeal for victims in particular. If you have been the victim of any crime from Sir Ted Heath or any historical sexual offence, or you are a witness or you have any information about this, then please come forward."
Wiltshire Police said Sir Edward "lived in Salisbury for many years".
It said: "We would like to hear from anyone who has any relevant information that may assist us in our inquiries or anyone who believes they may have been a victim."
Labour MP Tom Watson said he received information relating to allegations of child abuse involving Sir Edward in 2012.
"A separate claim concerning Heath was made to me subsequently," he said.
"I passed them both to the police, who have confirmed to me that at least one of those allegations is being investigated and taken seriously."
The Sir Edward Heath Charitable Foundation said: "We welcome the investigation by Wiltshire Police, which we wholeheartedly believe will clear Sir Edward's name and we will co-operate fully with the police in their inquiries."
Sir Edward, who led the Conservative government between 1970 and 1974, never married and kept his private life under wraps.
One biographer concluded that he may have been a "latent or repressed homosexual" while another thought he was "pretty well sexless".
Away from politics he was noted for his enthusiasm for sailing and classical music.
Sir Edward died at home in Salisbury aged 89 in July 2005.