An alleged cover-up of child sex allegations against Sir Edward Heath is at the centre of a police corruption probe.
Watchdogs are examining claims that a prosecution against an individual was shelved after a threat was made to "expose" the former prime minister.
The Independent Police Complaints Commission (IPCC) is also looking into whether Wiltshire Police followed up the claim against Sir Edward, which was made in the 1990s.
The inquiry was sparked by allegations made by a retired senior officer.
Meanwhile, Wiltshire Police have appealed for potential victims to come forward.
Sir Edward, who was PM for four years in the 1970s, is the highest-profile figure to be embroiled in historic abuse allegations against prominent figures.
Superintendent Sean Memory 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."
In a statement, Wiltshire Police said Sir Edward "lived in Salisbury for many years".
It added: "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."
An IPCC spokesman said it is to investigate allegations concerning the force's handling of an "alleged claim of child sexual abuse made in the 1990s".
He added: "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."
Labour MP Tom Watson claimed he received information relating to allegations of child abuse involving Sir Edward in 2012.
He added: "A separate claim concerning Heath was made to me subsequently.
"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."
In a statement 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 was famously reticent about his private life.
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.