Jailed billionaire Sean Quinn is studying law and answering dozens of letters as he spends time behind bars.

Once Ireland’s richest man, Quinn is serving his sentence for contempt of court at the semi-open training unit at Dublin’s Mountjoy Prison.

The Irish Sun reports that Quinn has been flooded with letters of support since he was jailed as a result of his battle with the former Anglo Irish bank.

The paper also reports that Quinn is studying law ahead of his return to the courts in the New Year.

The 66-year-old Quinn, currently serving a nine week sentence, has concentrated on files connected to his ongoing court battles with the Irish Bank Resolution Corporation.

An insider told the paper: “Because of his age and a heart condition, Quinn does not have to get involved in a lot of the work that other inmates are doing.

“He is keeping his head down and spends a lot of time going through all the correspondence he is receiving.

“He has received many letters of support, but he also receives a lot of post in connection with his legal matters.”

Quinn is also taking advantage of the gym facilities on offer in Mountjoy.

The source added: “He hits the treadmill and bikes every day.”