Terry Lubbock, whose 31-year-old son Stuart died following a party at Mr Barrymore’s then-home in Roydon Essex on March 31 2001, said some people who were at the party must be living under “terrible” pressure.
He said he hopes that the pressure might soon tell and persuade someone with information to come forward.
“It’s almost exactly 20 years since Stuart died, but to me it seems like last week,” Mr Lubbock, 76, of Harlow Essex, told the PA news agency.
“It must be exactly the same for all those people who were at the party on that night Stuart died.
“One of them at least must know something which they’ve never told, probably more than one.
“This never goes away because Barrymore is so famous, I won’t let it go away and media won’t let go away, and it must be hell living with that every day and every night.
“The pressure they must live under must be terrible.
“The 20th anniversary is approaching, I imagine there’s going to be a lot more publicity in the next couple of weeks, the pressure’s going to mount.
“I wouldn’t be surprised if someone cracks soon under all this pressure and decides to get it off their chest once and for all.”
Mr Lubbock wants a coroner to oversee a new inquest.
He said he thinks information has now emerged which would justify a second inquest.
A coroner recorded an open verdict after an inquest in 2002 and, in January 2018, the then-attorney general, Jeremy Wright, refused to give Mr Lubbock the go-ahead to make an application to the High Court for a second inquest.
But Mr Lubbock said a fresh Essex Police appeal, which coincided with the broadcast of a Channel 4 documentary Barrymore: The Body In The Pool, in February 2020, has changed the landscape.
A senior detective told reporters in early 2020 that he believed Stuart Lubbock had been raped and murdered and that “one or more” of the party-goers was responsible for “that serious sexual assault”.
He said lawyers, including barrister Alan Payne QC, are gathering evidence to support a bid for a new inquest. A friend of Mr Lubbock said supporters had provided money to fund lawyers.
“We have some big guns working on this,” added Mr Lubbock. “I’m hopeful that there will be a second inquest.”
He added: “I’d like to see Barrymore and the people at the party questioned at a new inquest, and see what they say when all this new information is put to them.”
Mr Lubbock said earlier this year that he had terminal cancer and doctors had told him that he might only have months to live.
No-one has been charged with any offence in relation to Stuart Lubbock’s death.
Mr Barrymore, now 68, was arrested in 2007 but never charged with any offence.
In March 2020, Mr Barrymore spoke to ITV’s Good Morning Britain programme and described the Channel 4 documentary as “vile and vicious”.
Mr Barrymore said nobody who was at his house on the night of Stuart Lubbock’s death knew what happened.
Asked if he had anything fresh to offer the police, he replied: “I honestly wish I did.”
He said he had been “through 20 years of hell”.
Essex Police have said their investigation is continuing.