Brigit is thrilled to be delivering Bennett’s one-liners

“I’m having a wonderful time,” says Forsyth, 73, who plays the part of Iris in Bennett’s gentle comedy set in a crumbling south Yorkshire stately home. “He writes such great parts for women, particularly older women.” Forsyth’s role in the play is as the loyal companion of aristocratic former model Dorothy (Sian Phillips) who is coming under pressure from her efficient archdeacon sister to hand over their dilapidated mansion into the care of the National Trust.

Dorothy, however, resists and comes up with her own more creative ideas on what to do with the place. Forsyth is having a tremendous amount of fun with her part and many reviews have mentioned that her character has some of the play’s best killer one-liners.

“When I read the play I thought ‘am I really going to be allowed to do this?’” she laughs. “She doesn’t say very much but then comes in with a golden line. The dialogue is such a joy to listen to – Alan Bennett’s work is as good as it gets.” The play’s sell-out run at the National Theatre is testament to that and the touring production has been equally well-received. “We’ve had terrific audiences,” says Forsyth. “And I’m loving every minute of it.” She modestly describes how surprised she was to get the part. “It was quite extraordinary,” she says. “I had booked a holiday with my son and his wife and my three grandchildren in Sardinia and my daughter-in-law asked me what would happen if I was offered work. I said there was only one thing that would make me give up the holiday and that was if the National Theatre got in touch because I had always wanted to work with them. Then my agent rang and said I was being considered for the part in People – I couldn’t believe it!” Still probably best known for her role as Thelma, the social climbing, controlling wife of Bob (Rodney Bewes), in the hugely popular 1970s sitcom Whatever Happened to the Likely Lads? Forsyth says that she would prefer to be recognised for the many and varied theatres roles she has played over the years – including a memorable Gertrude to Christopher Eccleston’s Hamlet in the West Yorkshire Playhouse’s 2002 production – but acknowledges that it has been a boost to her career. “I realise that it is my identity,” she says. “Thelma was a great part and the scripts were wonderful. I am a great realist and I know that if I hadn’t had Thelma, I wouldn’t get as much work as I do.” She is still offered plenty of parts in theatre and television and when there is a lull she has a new sideline to keep her busy – as a cellist in a band called the Fircones.

Forsyth, who has played the cello since she was a child, was invited to join the band which was formed by a group of actors who all appeared together in the original Calendar Girls stage show in the West End in 2009. They perform regular gigs around London. “I just love it because it’s a completely different side of me,” she says. “If someone had said to me ten years ago ‘you will be playing in a band’ I wouldn’t have believed them. It’s the same with working with the National Theatre – I had given up on that. So, anything can happen – it gives you hope.”

People, Leeds Grand, November 5-9. Tickets on 0844 848 2700.