He pleaded guilty at London's Southwark Crown Court to 10 indecent assaults on boys, a charge of gross indecency with a boy and another of indecency with a boy under the age of 14.
Denning, 73, had already pleaded guilty to 28 counts of indecent assault. He carried out this abuse over 20 years.
|BBC DJ Chris Denning 1964|
The ex-DJ was first arrested by detectives from the Metropolitan Police's abuse inquiry Operation Yewtree in June 2013.
Denning's 40 offences were committed between 1967 and 1987 and relate to 26 young male victims.
Two counts of indecent assault on a male aged 16 years or over between 1982 and 1983 were left to lie on file.
He had previously been jailed for four-and-a-half years in the Czech Republic in 2000 for having sexual contact with under-age teenage boys.
And he was jailed again in 2006 for four years after pleading guilty to child abuse during the 1970s and 80s.
'Bravery and courage'
Det Ch Insp Michael Orchard, from the Met's sexual offences, exploitation and child abuse command, said of his latest conviction: "Christopher Denning is a dangerous, serial offender who committed numerous offences over a 20-year period against a large number of young boys.
"One of these victims was as young as nine years of age. Denning's only redeeming quality is that he has not made his victims go through the trial process.
"I would like to thank the victims for their bravery and courage in coming forward. I hope that Denning's admittance of guilt is the first step in helping them move on with their lives."
Baljit Ubhey, chief crown prosecutor for the Crown Prosecution Service in London, said the scale of Denning's child abuse was "truly shocking".
"The compelling evidence in this case left Chris Denning with little option but to plead guilty," he added.
|Denning is now 73|
Denning, of Basildon, Essex, was one of the original line-up of Radio 1 DJs when the station launched in 1967.
He was also the first announcer heard on BBC2 when the television channel began broadcasting in 1964.
Operation Yewtree is the Met's investigation into the allegations that have arisen since DJ and presenter Jimmy Savile was accused of abuse.
The operation has three strands. One is looking specifically at the actions of Savile, the second concerns allegations against "Savile and others".
The third strand relates to alleged complaints against other people unconnected to the Savile investigations.