BRITAIN'S most notorious lag Charles Bronson was reportedly involved in a bust-up with a murderer while on the wing of his high-security jail.
Bronson, 71, is understood to have landed four punches on Robert Donaldson after being ambushed by the killer.
Donaldson had charged at Bronson, who has spent 50 years behind bars, leading to a bust-up, reports.
The Ministry of Justice confirmed they were investigating an incident at Category A HMP Woodhill in Milton Keynes, Buckinghamshire.
A spokesman said: "We do not tolerate violence in prisons and anyone who breaks the rules will be punished.
"It would be inappropriate to comment further while investigations are ongoing."
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The attack allegedly erupted on Monday - despite Bronson's previous attempts to avoid Donaldson.
The killer was jailed for murdering a man in 2005, as well as gagging a deaf 100-year-old woman and beating her elderly son.
Donaldson is said to have lunged towards Bronson with his fists raised.
Bronson then landed two hooks and two uppercuts on the murderer.
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He now reportedly fears the brawl could affect his next parole bid in ten months.
Last March, Bronson lost his eighth bid for freedom after spending nearly half a century behind bars.
Bronson's vile rap sheet includes holding 11 people hostage across nine sieges - including governors, doctors and even his own solicitor.
He was first jailed, aged 21, for seven years in 1974 after being convicted of armed robbery.
He later attempted to strangle inmate Gordon Robinson while at secure psychiatric hospital Broadmoor, before causing £250,000 worth of damage when he staged a three-day protest on a rooftop.
The lag was released in 1987 but soon returned a year later for intent to commit robbery.
After holding three men hostage in his cell, the criminal saw another five years added to his sentence.
Following further acts of violence behind bars, he was finally given a life sentence after kidnapping prison teacher Phil Danielson in 1999.
Bronson was further sentenced to three years for assaulting a prison governor in 2014.