Sir Richard never liked the National's full name

The two former directors joined Nunn at the theatre on London's South Bank for an onstage interview organised as part of the venue's 25th anniversary celebrations.

Sir Richard - who was director from 1988 to 1997 - said: "I find Royal National Theatre an oxymoron and I regret it."

He revealed how Labour peers Lord Rayne and Lord Mishcon - theatre board members at the time - had insisted on the "Royal" after the theatre put on Alan Bennett's A Question of Attribution in 1988.

Lord Rayne in particular thought the "Royal" would help counter criticism against the theatre in its early years, he added.

The theatre is on London's South Bank

Sir Richard also paid tribute to the late celebrated actor Lord Laurence Olivier, founder of the National Theatre.

"Without him we wouldn't be sitting here," Sir Richard concluded.

Play

Anniversary celebrations - from performances to guest appearances - have been going on for several months.

On Friday, the theatre stages a play written by 25 playwrights, who wrote a scene each.

The play, which is still under the working title of The Chain Play, was written by playwrights including Patrick Marber, Stephen Sondheim, Jonathan Harvey and Shelagh Stephenson.

Lord Olivier: Theatre's founder

It has been published scene by scene on the National's website. Actors taking part in the play include Tim McInnerny, Nichola McAuliffe and Simon Day.

Other celebrations have included an ongoing discussion series on the theatre's history called the the N25 Story with star contributors.

Still to come is an appearance by actress Joan Plowright, 70, who will talk about her life and career in the theatre named after her late husband Lord Laurence Olivier.

The National moved to its permanent home on the South Bank in 1976, after spending its first 12 years at London's Old Vic.