Police said they owed it to Mr Lubbock’s family to find the truth.
Assistant Chief Constable Tim Smith, head of the Kent and Essex Serious Crime Directorate, said: “The investigation into Stuart’s death, and how he sustained such serious injuries, is still open.”
A police spokesman added: “The passing of time can mean that loyalties change, and we would urge anyone who now wishes to come forward to us with information about Stuart’s death to do so – it’s never too late to do the right thing.”
Mr Lubbock’s body was found in the pool in Roydon, Essex, after a party in which drugs and alcohol were taken.
A post-mortem examination revealed he had suffered sexual assault injuries.
In 2007 Barrymore was arrested in connection with the death, but was later released without charge, and withdrew from public life..
His arrest found to be unlawful because the arresting officer did not have reasonable grounds to suspect Barrymore, a high court judge ruled.
Barrymore, now 67, fled and then stayed silent during an inquest into Mr Lubbock’s death.
He told Morgan he had left his home in fear that it would be “surrounded” by press.
He added: “I didn’t facilitate him taking drugs. I was advised (to stay silent) by lawyers at the time. You don’t have to answer in a coroner’s court.”
Recalling the events, he said: “That family deserves proper answers. No parent should have to bury their young.”
Barrymore told Morgan he hoped for “an answer (about Mr Lubbock’s death) within what is left of my life”.
Piers Morgan’s Life Stories featuring Michael Barrymore airs on ITV at 21:35 BST on Saturday 8 June
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