The two friends were chatting onstage before their first act and became so engrossed in the conversation, they missed the curtain-up call and found themselves acting out the insertion of a catheter for a packed theatre.

Stewart explains, "Ian and I were both onstage when the curtain went up... and this night I had been telling Ian, 'I'm having to see this urologist and he's putting this stuff into my bladder... with a catheter'. I said, 'It's a little strange but I've got used to it. The man who's doing it is a friend of mine, so it's all within the family'.

"And Ian said, 'Well, you know, I do that to myself... I don't have to go and see someone else; let me show you how I do it'.

"I am fascinated by this, so the two of us are standing onstage and he is showing me... and I'm standing there looking... and we had missed hearing the stage manager say, 'Standby, curtain going up', and it went up, while we were in mid-action."

Stewart fears the unguarded moment was more embarrassing for theatregoers than it was for them, adding, "I think Harold Pinter would have loved that moment."