Sir Edward Heath was "completely asexual", according to one of the former prime minister's closest advisers.
Lord Armstrong of Ilminster said child sex abuse allegations levelled at Sir Edward were "totally uncharacteristic and unlikely".
The late politician is being investigated by seven police forces over the claims as the police watchdog probes Wiltshire Police over whether a report of abuse, allegedly made in the 1990s, was followed up properly.
The late Prime Minister is being investigated by a number of police forces
Lord Armstrong, the Conservative leader's principal private secretary during his time as prime minister from 1970 to 1974, told the BBC he "never felt a whiff of sexuality about Ted Heath, whether it was in relation to women, men or children".
He said: "I knew him for 35 years, I worked very closely with him while he was prime minister and we remained friends for the rest of his life.
"You usually detect some sense of sexuality when you are friends or work closely with them. I think he was completely asexual. There are some people like that and I think he was one of them."
Speaking on BBC Radio 4's Today Programme, Lord Armstrong said that he believed claims that Heath was involved in abuse to be "totally untrue".
He added: "It seemed to be so totally uncharacteristic and so unlikely."
He also criticised the police investigation into the allegations, saying forces should not have gone public without specifying exactly what they were investigating.
The claims were unlikely because Sir Edward was under the guard of Scotland Yard protection officers when at home and did not drive, Lord Armstrong added.
"It just seems to me highly unlikely that he could have escaped all that to do the kind of thing that is described," he said.
His comments come after a former brothel keeper claimed she had arranged male escorts for the former premier.
Myra Ling-Ling Forde, 67, said Sir Edward was a "shy gay man" but not a paedophile.
Sir Edward died at home in Salisbury at 89 in July 2005.