Terry Lubbock believes entertainer has not told police everything he knows about his son’s death in 2001

The father of a man found dead in Michael Barrymore’s swimming pool has said he believes the entertainer knows more than he has revealed.

Terry Lubbock, 74, called for the TV presenter to “clear your name” as Essex police and Crimestoppers offered a £20,000 reward for information.

His son Stuart Lubbock, 31, was found dead at Barrymore’s then home in Roydon, Essex on March 31 2001, after a party with five other men and three women.

Det Ch Ins Stephen Jennings told reporters at a press conference at Essex police headquarters in Chelmsford: “I believe that he was raped and murdered that night … One or more of those partygoers are responsible for that serious sexual assault on Stuart.”

He said three people arrested in connection with the death – which included Barrymore – had not been “completely eliminated” from inquiries, while the five other people were still being treated as witnesses.

The officer admitted mistakes were made in the initial investigation after items possibly used in the attack – including a pool thermometer and a doorhandle – vanished from the crime scene.

But he said he was now confident that the force would find the killer and finally secure a conviction, hoping that the reward and a new documentary will generate new leads after 19 years.

“We know not everyone at that party was responsible for what happened, but someone was. We also know that not everyone at that party may know what happened, but someone does,” he said.

“We want the people who do have information to come forward and talk to us. Nineteen years is a long time, loyalties change, and it is never too late to do the right thing. Some people also arrived at the scene in the hours after Stuart’s death. They may hold the key information and we would like to hear from them.

“It is also possible that individuals at the party may have told other people what happened that night.”

Lubbock is also confident that his son’s killer will finally be found, and thinks Barrymore could help. “I think it’s time he comes clean,” he said. “It’s time now, Michael. I think you know more about this than you have said.

“It’s time now for you to either clear your name or put your hands up to what happened, because you must know.”

His comments come ahead of a new programme charting the police’s investigation into the death: Barrymore: The Body in the Pool, to be aired on Channel 4 on Thursday. The documentary tells the story of the death through interviews with journalists, forensics experts and people who knew Stuart.

At the beginning of the 90-minute programme, the 999 call reporting the incident to police is played. The caller says: “A fella has drowned in the pool. We have got him out. There’s a party going on and someone has just gone out and found him. I think the geezer’s dead, mate.”

Last year Barrymore spoke about the death, telling Piers Morgan’s ITV show Life Stories that he “couldn’t be more sorry” for his behaviour that night, and that he is “100% innocent”.

He was arrested in 2007 but never charged with any offence.

He sued Essex police, claiming that his arrest was wrongful and had cost him about £2.5m in lost earnings. However, the court of appeal judges concluded that he would be entitled to only “nominal” damages.