Dame Esther Rantzen hands over the reins of her beloved ChildLine to daughter Rebecca

The campaigner told how “terrific mother” Rebecca Wilcox will step into her shoes immediately.

The decision comes less than a fortnight after Dame Esther, 83, told how “this is the Christmas I thought I wouldn’t see” after being diagnosed with stage four lung cancer in January.

Mum-of-two Rebecca, 43, will also train to become a counsellor for the charity.

Paying tribute to the redoubtable activist, she said: “ChildLine has always been the other member of our family and I feel like I have grown up with it. It may have been the favourite sibling.

“My eldest son has never been interested or proud of anything I have ever done, but the other day he asked when he could tell people I am going to do this and said, ‘I am really proud of you, Mummy’.”

Dame Esther was fronting the phenomenally popular That’s Life! which ran for 21 years and drew audiences of 18 million when she suggested to the BBC a programme dedicated to preventing child abuse.

The breakthrough programme, Childwatch, was screened with the aim of detecting and protecting as many children as possible before their lives were in danger.

When ChildLine launched it was immediately swamped with 50,000 calls to a free, 24-hour helpline. The 0800 1111 number was chosen because it was simple enough to be instantly memorable to children of five or six years old.

In 2006 ChildLine became part of the NSPCC, meaning the charity could plough extra resources into developing an online service and expanding to meet huge demand.

Before the merger, as many as 4,500 children were phoning the helpline daily, but only half the calls could be answered.

Four times as many girls contact ChildLine as boys. Half those who contact the service are aged between 12 and 15.

Dame Esther said: “ChildLine has always had a very special place in my heart ever since we launched in 1986. But I have been concerned I have not been able recently to listen to children, meet staff and volunteers and spread awareness of our crucial lifeline the way I used to, due to my own health issues.

“Rebecca and I both jumped at the idea, suggested by the NSPCC, that she should take on the role because she has known, respected and cared about ChildLine almost all her life. She is just as committed to child protection as her father and I have always been. She is a terrific mother herself and understands the issues facing children today. And of course, she will take with her my best wishes to every team she meets and works with.”

The lifelong campaigner went on to set up The Silver Line, Britain’s only around-the-clock loneliness helpline, in 2013.

Rebecca, who has children Benji, 11, and Alexander, 8, said: “When we got mum’s diagnosis we thought things would happen at a pace and I was trying to keep her alive – I wanted a personal memory. I was going to ask ChildLine to volunteer but never expected to be asked to do something so huge. I am possibly not aware of just how huge. I like denial, it’s something mum and I have in common.

“ChildLine is such a brilliant charity, it’s wholly unique, giving children a voice, and allowing them to speak.

“All those years ago I don’t think anyone realised there was a vacuum to be filled, yet there was still so much resistance towards trusting children and listening to them. It worried a lot of people, but mum has always enjoyed talking to children, possibly more than adults.

Her insights from sitting in on counselling sessions are such a precious resource. I cannot imagine living without them and cannot express how much I will need this in the future.

“It seems unfathomable to do this without her and her knowledge. I will feel like a pale ghost in comparison, but there is no way I could say no. I would have hugely regretted it.”

Dame Esther said some of the most rewarding moments of her life have been meeting adults who said they used ChildLine when they were young, and how support transformed their lives.

One, Charlotte, lived with an alcoholic stepfather who regularly beat her mother and step-sister. He threatened to kill her if she ever reported what he was doing.

It took her 10 attempts to call ChildLine, but she eventually plucked up the courage. As a result, the violent abuse stopped. She then joined ChildLine’s staff and is protecting and supporting children as vulnerable as she once was herself.

Dame Esther said: “Charlotte’s story is proof of what I call the upward spiral. Children who have received timely and effective help when they needed it most never forget it, and want to give back. As Rebecca puts it, saved children save other children. I believe the work ChildLine does day in, and day out, will rescue future generations of children from despair.

“ChildLine has been home to thousands of passionate, committed, professional and skilled volunteers. They are responsible for the transformation in millions of children’s lives. I may have been lucky enough to have had a lightbulb moment and come up with the idea, but I cannot claim anything more than that.”

Redoubtable Dame Esther is now looking forward to spending Christmas with Rebecca and her other two children, Miriam and Joshua, from her marriage to the late Desmond Wilcox, and her beloved grandchildren, which also induce Joshua’s three children Teddy, 8, and twins Florence and Romilly, 5.

Rebecca said: “My brother said living with mum is like living next to a volcano – you don’t know whether the flowing lava is going to be flowers and celebrations or explosions.

“She’s never done something to win our approval, it’s always because of what is right.

“Her early adoption of campaigns is probably the most underrated skill she has. She has a strange zeitgeist, even at 83. She is always on the money and always gets it. She is the person I ring several times a day and see several times a week. But hell hath no fury like Esther being told ‘no’.

“Christmas is going to be spectacular and there will be more food, crackers, sparkly lights, and presents than she could ever want.”

Dame Esther said: “My diagnosis made me realise how very lucky I’ve been in my life, working with ChildLine and The Silver Line, and meeting so many fascinating and inspiring people.

“I’m not good at regrets. What I treasure most are my family and the fantastic friendships I have made thanks to That’s Life! during the last 50 years, the people I met, and the team who worked so hard, and laughed so hard, together for so long.”

Despite dedicating her life to helping others, Dame Esther has spoken about her own struggles after her documentary maker husband – the man she still lovingly refers to as “my Desi – died in 2000.

She said: “ChildLine proved to me that if you offer a way of safely providing help, people will use that resource.

“Not a day goes by when I don’t think of Desi. The passage of time doesn’t make it any easier. Yes, I am very busy, but I still get terribly lonely. It can strike everyone, rich or poor, unknown or famous.”

Peter Wanless, chief executive of NSPCC, said: “For more than 35 years Dame Esther has been the face and the heart of ChildLine, working tirelessly to set up, build and promote the service as a place where children and young people across the UK can go for free and confidential help and support. It is impossible to put into words the gratitude we feel for everything she does.

“We welcome Rebecca to her new role while we continue to keep Esther updated on all the great things ChildLine continues to deliver.”