The television star, artist and songwriter was jailed for five years and nine months in July last year.
He was found guilty of indecently assaulting four victims between 1969 and 1986, including the childhood best friend of his daughter Bindi.
The letter, which appeared in The Mail on Sunday newspaper, was reportedly written in February to a friend who was "so appalled at its contents" that he passed it to the weekly tabloid.
"At last after eight months inside, the inner rage has come to the fore. I've started writing a song about the injustice of it all," the letter said.
"I plan to record this the moment I get out towards the end of 2017," he wrote, envisaging a "country rock sound with a heavy backbeat".
It begins: "Climb up out of the woodwork babe, from 40 years ago,
"The climate's great in Britain now, for making loads of dough,
"You've festered down there long enough, time's right to grab your chance,
"Clap eyes on a rich celebrity and make the bastard dance."
The first chorus begins: "Make him squirm, slimy little woodworm".
One line reads: "Perhaps you believe you're pretty still, some perfumed sultry wench."
Other lines say: "Get your 50-year-old hooks into his dough.
"Come and join the feeding frenzy, girls."
Lawyer Liz Dux, who represented Harris's victims, said they would be "distraught" at the song, which showed he should be denied parole and be "made to serve his full sentence" in prison.
According to The Mail on Sunday, one of his victims said: "I am totally revolted by what he has written.
"He has shown no remorse and continues to think he can treat his victims like dirt. His arrogance is beyond belief. I am devastated by reading this and it will set back my recovery at a time when I am trying to rebuild my shattered life."
Harris was prosecuted as part of Operation Yewtree, which was set up in the wake of revelations that British TV presenter Jimmy Savile, a fellow major BBC star, was a prolific abuser.
Other celebrities have been convicted of historic sex offences as part of the operation.
Harris painted an 80th birthday portrait of Queen Elizabeth II in 2005 and took part in her diamond jubilee celebrations in 2012. He has been honoured by both Britain and Australia, though has since been stripped of his medals.
As a singer, he topped the Australian charts in 1960 with "Tie Me Kangaroo Down, Sport" and the British charts in 1969 with "Two Little Boys".
Media reports last month said England's state prosecutors were examining a file of further allegations against Harris.
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He was found guilty of indecently assaulting four victims between 1969 and 1986, including the childhood best friend of his daughter Bindi.
The letter, which appeared in The Mail on Sunday newspaper, was reportedly written in February to a friend who was "so appalled at its contents" that he passed it to the weekly tabloid.
"At last after eight months inside, the inner rage has come to the fore. I've started writing a song about the injustice of it all," the letter said.
"I plan to record this the moment I get out towards the end of 2017," he wrote, envisaging a "country rock sound with a heavy backbeat".
It begins: "Climb up out of the woodwork babe, from 40 years ago,
"The climate's great in Britain now, for making loads of dough,
"You've festered down there long enough, time's right to grab your chance,
"Clap eyes on a rich celebrity and make the bastard dance."
The first chorus begins: "Make him squirm, slimy little woodworm".
One line reads: "Perhaps you believe you're pretty still, some perfumed sultry wench."
Other lines say: "Get your 50-year-old hooks into his dough.
"Come and join the feeding frenzy, girls."
Lawyer Liz Dux, who represented Harris's victims, said they would be "distraught" at the song, which showed he should be denied parole and be "made to serve his full sentence" in prison.
According to The Mail on Sunday, one of his victims said: "I am totally revolted by what he has written.
"He has shown no remorse and continues to think he can treat his victims like dirt. His arrogance is beyond belief. I am devastated by reading this and it will set back my recovery at a time when I am trying to rebuild my shattered life."
Harris was prosecuted as part of Operation Yewtree, which was set up in the wake of revelations that British TV presenter Jimmy Savile, a fellow major BBC star, was a prolific abuser.
Other celebrities have been convicted of historic sex offences as part of the operation.
Harris painted an 80th birthday portrait of Queen Elizabeth II in 2005 and took part in her diamond jubilee celebrations in 2012. He has been honoured by both Britain and Australia, though has since been stripped of his medals.
As a singer, he topped the Australian charts in 1960 with "Tie Me Kangaroo Down, Sport" and the British charts in 1969 with "Two Little Boys".
Media reports last month said England's state prosecutors were examining a file of further allegations against Harris.
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