John Alford, 54, was jailed for eight-and-a-half years in January after he was found guilty of assaulting his victims at a party.
He died at HMP Bure on Friday, the Prison Service said.
HMP Bure, on the former site of the former RAF Coltishall base, is a specialist unit exclusively holding men convicted of sexual offences.
John Alford also starred in Grange Hill (Image: Peter Jordan/PA Wire)
The former actor, who also appeared in the BBC drama Grange Hill and whose real name was John Shannon, was convicted of four counts of sexual activity with a 14-year-old girl and charges of sexual assault and assault by penetration relating to a 15-year-old girl at a property in Hertfordshire on April 9, 2022.
After Alford’s death, a Prison Service spokesman said: “John Shannon died in prison on March 13, 2026.
“As with all deaths in custody, the Prisons and Probation Ombudsman will investigate.”
Jurors heard during the trial that the defendant sexually assaulted the girls while they were drunk following a night out at the pub.
St Albans Crown Court heard that Alford bought some £250 worth of food, alcohol and cigarettes from a nearby petrol station, including a bottle of vodka which the victims subsequently drank.
This photo was originally issued on 14/01/26 by Hertfordshire Police of John Alford, real name John Shannon (Image: Hertfordshire Police/PA Wire)
He then sexually assaulted the 14-year-old girl in the garden of the home and later in a downstairs toilet, and inappropriately touched the 15-year-old girl as she lay half asleep on the living room sofa.
Police received a third-party report from the 15-year-old girl’s mother outlining the allegations two days later.
The 15-year-old girl said in her evidence she had felt “absolutely sick” following the assault and had planned to keep the incident secret before having a “mental breakdown” to her friend’s mother on April 11.
Alford told jurors during the trial that all the allegations were “scandalous” and a “set-up”, and that there was no DNA evidence to support the assaults.
He said he had told police that the girls were “going to extort money” from him, and that he suffered from mental health issues, including anxiety, depression and paranoia.
Alford was previously convicted of supplying illicit drugs to former News of the World journalist Mazher Mahmood, who was known as the “fake sheikh”, following a trial in 1999, and was jailed for nine months.