The claims, if substantiated, are likely to result in a major civil action being taken against the state on behalf of the English journalist.

He was targeted by gardai as the chief suspect in du Plantier's killing.

Du Plantier was beaten to death at her holiday home at Toormore, Schull, Co Cork on 22/23 December 1996.

Nobody has ever been charged in relation to the murder.

The Sunday Tribune has learned that Bailey was interviewed by a team of gardai in recent weeks in relation to the alleged physical mistreatment in custody, as well as other key aspects of the handling of the murder investigation by gardai across several sections of the force.

The interviews were conducted as part of a probe into the initial garda murder investigation after a major witness in the du Plantier case publicly claimed that she had been pressurised by gardai into making false statements that she witnessed Bailey near the murder scene on the night the French woman was killed.

Farrell initially claimed that she was driving her car in the early hours of 23 December 1996 at Kealfada Bridge near the murdered woman's home when she saw Bailey walking along the road. Bailey repeatedly denied that he was near the scene of the murder at this time. However, Farrell has since claimed that her initial statement was incorrect and groundless.

She said she was conducting an affair with a man on the night in question and said that she was concerned that if she did not cooperate with gardai then members of the force might reveal details of the extra-marital relationship.

Garda commissioner Noel Conroy ordered a review of the murder investigation to be carried out following the change to Farrell's evidence, which she initially made to gardai following the murder, and subsequently during a 2004 civil action.

The Sunday Tribune understands that the garda review team has conducted four interviews with Bailey while Farrell has conducted two similar interviews. Another is scheduled for next week.

She has presented gardai with a dossier of information in support of her claims, according to sources close to the internal garda probe.

It is understood that the internal garda probe has been given a wide remit to include not only the initial investigation but also a later review by the National Bureau of Criminal Investigation in 2002.

Senior gardai expect that the internal review is likely to be completed by June.