Prison report: Sir David Ramsbotham

The pair returned 20 minutes later to explain the claim was a joke.

The wardens were immediately suspended while prison officials conducted an investigation and were subsequently dismissed.

A spokeswoman for Parc - which opened in 1997 at a cost of �82m - said the prison does not tolerate such behaviour.

Their actions "fell well below the duty of care that they should have had for inmates", she said.

The jail was criticised in a 1999 Prison Inspectorate report after it emerged a racist group with Ku Klux Klan links was running a wing, making it impossible to house black prisoners.

But the Chief Inspector of Prisons later lauded jail owners Securicor in March 2001 for measures taken to improve matters.

Sir David Ramsbottom said Parc Prison had gone on to develop very good systems to deal with sex offenders and drug addicts and to minimise suicides and bullying among its 835 inmates.

According to his report, the prison - which suffered a number of high profile problems and suicides by inmates after it opened - had "matured and progressed".

It had a "stable and secure environment" and anti-bullying schemes were in action throughout the jail, it was concluded.