Kavanagh, who is currently serving a 21-year sentence for drug trafficking was recently moved to the maximum security facility, for "security reasons".
He is now a resident of Her Majesty's Prison Belmarsh, the Category-A men's prison, located in Thamesmead, south-east London, that is primarily used for high-profile cases, particularly those concerning national security.
The 48 single-cell High Security Unit (HSU) within the prison is regarded as the most secure prison unit in the United Kingdom.
It was even the subject of a 2020 documentary, ‘Welcome To HMP Belmarsh’, featuring the actor Ross Kemp who examined what life was like in the Category A unit by talking to inmates to get their take on the conditions.
Built in 1991, the jail has been nicknamed ‘Britain’s Guantanamo Bay’ due to the number of terrorists and extremists it held behind its walls.
In recent years, Jordanian cleric Abu Qatada and Salafist preacher Anjem Choudary have all been housed there.
The prison's high-security unit includes inmates who need to be protected because of their offence and those who are regarded as being high-profile.
Among them is Michael Adebolajo, the man who murdered British soldier Lee Rigby nine years ago on the streets of London.
Adebolajo and Michael Adebowale were both sentenced to life for the savage killing which shocked the world.
Adebolajo received a whole life tariff meaning he will die in prison, while Adebowale received a 45-year tariff meaning he can’t apply for parole before then.
Another extremist, Ali Harbi Ali, a 25-year-old British man and Islamic State sympathiser, is also an inmate, after he was arrested at the scene of the killing of David Amess, a British Conservative Party MP.
Amess died after being stabbed multiple times at his constituency surgery at Belfairs Methodist Church Hall in Leigh-on-Sea, Essex.
Ali was later found guilty of murder and the preparation of terrorist acts in April 2022, and was sentenced to life imprisonment with a whole life order.
Julian Assange has been languishing in Belmarsh for the last three years, after Ecuador kicked him out of their embassy and he was promptly arrested for breaching bail.
The WikiLeaks founder has been kept at Belmarsh since May 2019 after he was sentenced to 50 weeks in prison for skipping bail.
In November 2019, a group of doctors claimed that Assange was at risk of dying in prison due to his poor mental and physical health.
He is currently facing extradition to the US under the 1917 Espionage Act after he helped he found WikiLeaks in 2006, which went on to an obtain and release classified or secret documents, infuriating governments and corporations around the world.
The jail also houses the notorious Grindr killer, Stephen Port.
In November 2016, Port was jailed for drugging and murdering men he met on gay dating app Grindr before dumping their bodies in a graveyard
Port's life and crimes were recently the subject of a BBC crime drama, called Four Lives, with Stephen Merchant portraying serial killer Port.
Former inmates of Belmarsh include Wayne Couzens who killed Sarah Everard (33) in March 2021 after Couzens stopped and handcuffed her in south London on the pretence she had broken lockdown rules.
Her burned body was later found in a pond near a patch of land he owned in a Kent wood.
Couzens is serving a whole-life sentence for the kidnap, rape and murder of the 33-year-old marketing executive in March last year, when he was a serving Metropolitan Police officer.
Couzens was moved from Belmarsh to Frankland Prison just before Christmas, and had been segregated on a wing for vulnerable inmates.
He was taken to hospital on his third day in custody, after being found unconscious in a cell at Wandsworth police station following a suicide attempt while he was awaiting trial.
He is said to have refused food and threatened to go on a hunger strike in protest at his supposed harsh treatment at the jail.
Another notorious killer who has been moved to Frankland after spending time at Belmarsh is Ian Huntley, who committed the horrific Soham murders in August 2002.
The victims, two 10-year-old girls, Holly Marie Wells and Jessica Aimee Chapman, had been lured into the home of the local resident and school caretaker, who subsequently murdered the children before disposing of their bodies in an irrigation ditch close to RAF Lakenheath, Suffolk.
On August 20 Huntley was charged with two counts of murder and sentenced to two terms of life imprisonment, with a minimum of 40 years behind bars.
Huntley who was later transferred to HMP Wakefield before being moved again to HMP Frankland in 2008, will not be considered for release until 2042 at the earliest.
The murderer is at constant risk of attack from other prisoners and has had a string of health problems and suicide attempts behind bars.
Tommy Robinson, the founder of the British Defence League and far right extremist – real name Stephen Yaxley-Lennon was released from Belmarsh in 2020 after serving half of his 19 week sentence for contempt of court.
Upon his release, Robinson was reported as saying he had been put in solitary confinement during his time in the unit.
“I walked into Belmarsh prison and walked out without seeing another prisoner … for my safety,” he said.
Anjem Choudary spent time at HMP Belmarsh ahead of his release in 2018. The Islamist preacher was sentenced to five years and six months in prison in 2016 after being found guilty under section 12 of the Terrorism Act 2000 for inviting support of a proscribed organisation. But he only served half of his original sentence.
Ronnie Biggs spent time in Belmarsh following his return to the UK from Brazil where he fled following his escape from Wandsworth prison in 1965.
The train robber remained there for six years until he was transferred to Norwich Prison on compassionate grounds due to his failing health.
Jeffrey Archer spent less than a month in Belmarsh, but he still documented his time there and later published his experience in the three volume book, A Prison Diary, which detailed his time in three separate prisons. The disgraced politician described Belmarsh in the book as a “hell hole”.
Charles Bronson, dubbed Britain’s most violent prisoner, has spent numerous periods of time in Belmarsh since being sentenced for armed robbery in 1976 – bar a brief period of freedom.
During his time at Belmarsh, he took three other prisoners hostage.