Dame Diana Rigg has confessed she struggled to keep a straight face acting with her daughter in Doctor Who.
The 74-year-old actress - who made her name in roles such as leather-clad, karate-chopping Emma Peel in The Avengers and in the 1969 James Bond film On Her Majesty's Secret Service - appears in the sci fi drama this week with her daughter Rachel Stirling.
Dame Diana said: "Rachie and I had great difficulty keeping a straight face in some scenes. Hopefully we're believable. I play a horrendous old bag who wants to take over the world. I love playing old bats....
"I don't think there's any competition between us. Each generation has to re-interpret the great parts for themselves, which is why the theatre remains fresh. It was mad to resist her desire to act. I say, 'Go ahead, do your stuff.' I've handed her the baton, but as any mother will tell you, 'Keep your mouth shut.' She does what she wants, is strong and good, and has my total approval."
The actress, who also stars in Game of Thrones, said: "Actors are very lucky that an audience comes along and is prepared to believe in us. It's an act of faith.
"But your career cannot be your life. I've met women who are hungry for every part and don't feel they exist unless they have a series of jobs lined up. They imbue acting with an importance which, frankly, it doesn't have. Sad cases."
Dame Diana also revealed that she had never turned her back on The Avengers.
"It's true I'm not big on reunions, and fans get miffed when I don't turn up, but it made me well known worldwide. I'd have had to spend 150 years touring to get such an audience. Fully grown, not to say 'mature', gentlemen, come up and say, 'I saw you when I was a boy'", she said.
"I don't mind getting older, but people don't tell you it's painful. And if you're acting, you can't afford to show it. I had a knee operation not long before I did Doctor Who so I wasn't terribly mobile but I had to be, which is no bad thing because you force yourself to exercise.
"I saw Billy Connolly doing a sketch about the noises old people make getting out of a chair, so now I shed the years and spring out silently."