Prison officers want an inquiry after a recording of Charles Bronson's voice was played at the premiere of a movie about the long-serving inmate's life.
The armed robber and hostage taker, 56, made the recording at high-security Wakefield prison, in West Yorkshire.
He told the London screening of Bronson: "See you at the Oscars".
The Prison Officers' Association said the recording undermined prison security. The government said steps had been taken to prevent a repeat.
The Ministry of Justice said any interviews with the prisoner contravened Prison Service policy.
Bronson has spent virtually all of the past 35 years in jail, having originally been sentenced to seven years for armed robbery in 1974.
He has carried out a string of crimes in prison, including hostage-taking, assaults and rooftop protests, and has spent much of his time in solitary confinement.
However, he is expected to go before the Parole Board in an attempt to win his freedom on Wednesday.
In the recording, he told the audience at Tuesday night's premiere: "I'm proud of this film, because if I drop dead tonight, then I live on," before adding: "As long as my mother enjoys the film, I'm happy."
Bronson, who was born Michael Peterson in Aberystwyth, said: "I make no bones about it, I really was... a horrible, violent, nasty man.
"I'm not proud of it, but I'm not ashamed of it either, because every punch I've ever flung in my life I've taken 21 back."
Bronson's family and friends called for his release at the premiere, saying he was a changed man.
His mother Eira Peterson, 78, said: "He's very different now, he's not a danger to anybody, he's mellowed right down.
"I just want him to come out now and make a new life for himself before I pass away."
The Prison Officers' Association has condemned the movie - starring Tom Hardy in the title role and released on Friday - for glorifying violence.
Calling for an investigation into the recording, full-time officer Glyn Travis said: "We've got grave concerns that people have abused the privilege of speaking to and visiting Charles Bronson while in prison.
"As a result of that they have managed to secrete or record a telephone call or conversation which has now been played in a public forum.
"Clearly somebody has abused the rules."
The prison's policy says all visitors must be approved in advance before being allowed in, and phone calls are recorded.
A Ministry of Justice spokesman stressed it and the Prison Service had not had any involvement in the making of the film.
He added: "The Prison Service has taken appropriate steps to ensure that Charles Bronson does not profit financially from this film while he remains in prison.
"Any unauthorised interviews with the prisoner have been made in direct contravention of Prison Service policy. Steps have been taken to ensure that this does not happen again."
Actor Hardy has said he would like to see Bronson out of prison, claiming he found him "warm, articulate, kind, intelligent, funny and charismatic."
Director Nicolas Winding Refn denied that the film glorified violence.