Jack Straw, Secretary of State of Justice, stepped in to cancel the eight-day comedy workshop as soon as he heard about it and said prisons should be about punishment, reform and education.

He said: "I instructed that it must be immediately cancelled. It is totally unacceptable. Senior managers in the Prison Service, who were also unaware of the course, take the same view as me.

"Prisons should be places of punishment and reform, and providing educational, training and constructive pursuits is an essential part of this. But the types of courses available, and the manner in which they are delivered, must be appropriate in every prison.

"What happens inside the prison gates has ramifications outside, on victims and their families, and on taxpayers. There is a crucial test: can the recreational, social and educational classes paid for out of taxpayers' money (or otherwise) be justified to the community?"

A Ministry of Justice spokesman added: "The director of high security prisons is conducting an investigation to establish the facts and to determine appropriate action.

"Today (Friday), the Director General of the National Offender Management Service is personally briefing governors from all prisons on the need to take account of the public acceptability test."

Comedy classes, which organisers say boost team work and communication skills, have been available at the prison since 1998.