Non-Muslims in some of the United Kingdom’s maximum security prisons have reportedly been bullied into paying a tax for their protection from radical Muslim prisoners, who are running prison life in accordance with their own rules and Shariah law. Some inmates said they have paid the tax, known as “jizya,” because they feared being attacked by other inmates who have aligned themselves with the so-called Islamic State (aka ISIS), a Sunni Muslim terror group operating in Iraq, Syria and other countries in the region.

The jizya payments had been enforced by some Islamic extremists prisons inside of four British prisons, the Daily Express reported Monday. Government investigators appointed to identify threats posed by Islamic extremist inmates in U.K. prisons uncovered the scheme.

Steve Gillian, general secretary of the Prison Officers’ Association, a London-based national union, said prisons have struggled with the radicalization of inmates. “People at times are bullied and intimidated and harassed into becoming a Muslim, and if they don't, they are attacked,” he said, according to the Daily Express report.

Gillian added: "There is a massive issue about radicalization and extremism and, to be fair, the prison service is trying to address it. Will it go away? No. I think the assumption is that it will get worse.”

The officials’ investigation, which began in August,  found that inmates have often used tobacco and other items smuggled into prisons to pay off extremist prisoners. Some inmates reportedly have sought financial help from family and friends to pay the tax. 

The investigation team examined Belmarsh, Long Lartin, Woodhill and Whitemoor prisons -- all “Class A,” or high-security, prisons that hold a total of 2,633 inmates, according to the Daily Express. The Belmarsh prison had previously held high-profile Muslim clerics, including Abu Qatada, who was held there before his deportation to Jordan.