Dame Esther Rantzen talks to Wayne Savage about her debut UK tour and what it’s like being grilled live on stage by her daughter Rebecca Wilcox.

There are only two topics off the table when Esther and Rebecca chat. The first is Brexit, which whips people on both sides of the argument into an almost religious fervour. The other is sex.

“It makes her feel sick if I even mention it so I won’t. I think nobody wants their mother to talk about sex,” laughs the legendary broadcaster.

A good way out when she’s looking to deflect a challenging question though?

“She’s a really good interviewer and asks me things which are quite difficult to answer; who else would dare ask them? There are very few fixed points in the show but one - because I never answer the question, not yet - is ‘mum, you worked with Princess Diana on ChildLine and you are currently working with Camilla, Duchess of Cornwall on The Silver Line; which do you prefer?’ The whole audience goes ‘oohhh’. So that’s a very wicked suggestion but if she gives me a hard time I may well bring the subject up.”

Esther is full of praise for Rebecca, a respected TV investigative and consumer journalist. She knows there’s no getting away with a bluff or a deceitful answer when the interviewer knows the truth. It also means mum can turn the tables, asking her daughter things she wouldn’t in an everyday conversation.

“For example, I was working all the way through her childhood and I want to know whether she feels she missed out. The fact her father (acclaimed British documentary maker Desmond Wilcox) and I were both working very hard in television must have given her a taste for it because she’s in it and she’s a very good reporter. In another way, she’s decided to be a full-time mum so you could say she’s looked at my pattern and decided its not for her.”

The duo have a very strong relationship, as did Esther with her own mother and she with hers.

“When you get that sort of closeness... my mum died at 94 but right up to the very end I always used to spend my weekends with her. I’m incredibly close with all my children. I think you either have that inherited from your own parents or you’ve got to build it from scratch and I’m very lucky I’ve had that example in my own family life.”

Rebecca, who has two little boys bustling with energy, has become quite protective of 78-year-old Esther; who finds it touching. That fades in front of an audience though.

“Then it’s no holds barred,” she laughs. “I enjoy that too because it makes me laugh, when she says something quite naughty, sending me up. It’s also interesting, seeing her memories. What we do in the show is explore iconic moments like one particular sequence from That’s Life which has gone onto YouTube and been viewed millions of times.

“That’s the story of Sir Nicholas Winton, who we brought into the studio and sat him with the (grown up) children he rescued from The Holocaust. They didn’t know him and they met for the first time. That sort of moment moves her, moves me, moves the audience every time so it’s interesting, we cover the whole range.”

The show looks back at both their careers as well as offering a candid insight into their family and personal life, with outrageous stories from Esther’s 50 years in broadcasting.

A national TV treasure, tireless campaigner and philanthropist; she’s perhaps best known for her record-breaking 21-year stint on the iconic BBC1 TV magazine series That’s Life. A show that championed unusually shaped veg long before it was fashionable.

“There was a time when the EU banned them. I’m not venturing into Brexit, but now it’s relented so the parsnips are back to my pleasure. I always blamed the viewers...,” says Esther, who’s enjoying an éclair with her feet up when I call. Her daughters joke she won’t eat anything that wasn’t invented before 1950.

Approached by a distinguished academic keen to highlight the series’ impact on modern telly, she’s gathering letters, documents and scripts she’s been hoarding. It changed lives for the better too don’t forget.

“That’s quite true, it changed the law on things like seatbelts in the backs of cars for children, the way our playgrounds were built so instead of concrete and Tarmac we had soft services...”

Not everything was for the better though.

“We invented Simon Cowell. We did a series called Search For A Star and he was our record producer. Some people say we even invented the reality show because everything we showed came from viewers. Even when we were making films it was all real and entertainment created for us.

“I’m not sure if I want to claim I invented the reality show but it was certainly there. What’s happened since is other programmes have taken strands from what That’s Life did but there isn’t another programme that combines them all, the tears, the laughter. The thing about today’s shows is they are far more predictable in a sense. You haven’t got the cliché of the rollercoaster, you’re either going uphill or downhill; you very rarely do both.”

The other thing of which she’s most proud is the campaigning and charity work which has transformed countless lives.

She founded ChildLine in 1986, the first national helpline for children in danger or distress. In 2013 she set up The Silver Line to help combat isolation and loneliness in older people. Her work has earned her an OBE for services to broadcasting, a CBE for services to children and a DBE for services both to children and older people.

“I can’t claim the credit. ChildLine has helped four-and-a-half million children. The Silver Line has taken two million calls. Obviously I haven’t done that, it’s the dedicated and skilled volunteers but I’m thrilled to have been part of that.

“The television side has been exciting and fun and challenging. It’s taken me into places and allowed me to meet people and I could never have had that adventure without having that job so I’m really grateful, but television comes and goes. What I’m hoping is that ChildLine and The Silver Line thanks to the work done by others will be there forever.”

Esther loves working to a live audience, jokingly likening herself to an old racehorse whose adrenalin kicks in at the starting gate and has to pound her way to finishing line. She loves hearing the audience listening, sometimes snoring and the more they give back in terms of questions and comments, the more fun everybody has. She must have been asked some strange questions.

“I was in Norwich and a lady said to me ‘who is the maddest person you ever interviewed’. I looked at her and she said ‘for example, a lady who ate wood’ and it was her daughter. I had seen Christine 30 years before but she was so memorable, she could tell the difference between an oak an and an elm just by eating bits of bark. Only in Norfolk...”

• See Esther Rantzen and Rebecca Wilcox in That’s Life at Norwich Playhouse, October 20.