An Irishman jailed for operating a $1.5 million-a-year international prostitution ring has condemned what he calls the 'racist' British prison that has prevented him from flying an Irish tricolor in his cell.

Thomas Carroll, 50, was jailed for seven years at Cardiff Crown Court in Wales in 2010 after pleading guilty to running a network of 18 brothels in Northern Ireland and the Republic.

According to the Belfast Telegraph, Carroll and his South African wife Shamiela Clark forced up to 70 women to work as prostitutes after they were trafficked into Ireland from Europe, South America and Nigeria.

The couple reportedly ran a 'call centre' from a former vicarage in Wales where they made deals with sex traffickers. The unsuspecting women had been told they would find work as hairdressers and seamstresses in Ireland.

Carroll and Clark sent the women to rented apartments in Northern Ireland and the Republic where they were told to wait for clients.

The couple earned around $1.5 million-a-year from their 15 brothels in the Republic and three in Northern Ireland, the court heard.

Now a prisoner in Wales, Carroll is complaining that the prison he is incarcerated in is discriminating against him.

'Upon having a paper flag taken from my cell wall by a prison employee I requested that my family send a flag in by mail,' Carroll wrote in a letter to the prisoners' newspaper Inside Time.

'But when it arrived the authorities refused to let me have it because it constitutes a 'security issue.'

Carroll, originally from Bagenalstown in County Carlow, wrote: 'As a proud nationalist and republican, I deem it to be my right, as it is the right of any of my countrymen and women, to be in possession of our national flag. The refusal to allow me my flag is discriminatory and racist. I respect the fact that I am in a British prison and would only have displayed my flag in my own cell and not in public view.

'My ancestors fought for the right to fly our national flag and… I reserve the right to fly the Irish tricolor wherever I may be.'

A spokesman for the prison told the press they were investigating Carroll's claims.