Sir David Ramsbotham made the remarks during a speech at a conference on the problem of drugs in jails at Aston University, in Birmingham.

This is a grossly offensive and racist insult

Ron Adams, Prison Officers' Association

Vice-chairman of the Prison Officers' Association Ron Adams has called for Sir David, who was appointed Chief Inspector of Prisons five years ago, to be sacked.

"This is a grossly offensive and racist insult considering that 28 Irish prison officers have been murdered by the IRA since the troubles began," Mr Adams told the Sun newspaper.

Sir David, 66, told his audience the following joke:

Paddy One: We have not put enough glue on to seal these letter bombs.

Paddy Two: We will have to open them up again and then reseal them.

Paddy One: If we do we will be blown up.

Paddy Two: No we won't - they are not addressed to us.

'Unbelievable'

The Home Office refused to comment on Sir David's joke.

But a member of the audience said his comments were unbelievable, adding: "No one could believe what he had said.

What is a man in his position doing making anti-Irish jokes?"

Sir David is perhaps better known for his outspoken and often damning reports criticising prison regimes.

And he has not shied away from criticising senior prison management for "failure of leadership", saying the "culture of cynicism among senior officers pervades the prison service and stifles progress".