She was 68 years old; it must have been drooping for years.

But the love-blinkered way in which our beloved sees us becomes the way we view ourselves.

Sheila's ignorant bliss as to the effects of gravity and time were testament not to the miraculous, lifting properties of Lycra Bridget Jones pants, but to the miraculous, lifting powers of love.

Because John Thaw constantly told his wife how beautiful she was, quite naturally, she believed it.

"I never challenged his view that I was attractive. I hadn't noticed that things were going south," she says, laughing now, 75 and still a beautiful woman.

She made the brutal discovery about her bottom while on her first solo holiday – the one she had forced herself to go on to snap herself out of a looming depression.

There she was, sunbathing at a posh Italian hotel, surrounded by gorgeous, glamorous young couples.

It was lavish, luxurious.

She felt alone, old.

"Waiters were circulating, serving drinks. It is a proven fact that after 50, women do dissolve," she says in her latest book, Just Me.

She watched svelte girls sashaying to the pool and felt rooted to the sunbed: "If John had been there, I would not have thought twice of bounding down and plunging in for a swim. Without his loving gaze I recognise the stark reality of the damage wrought by gravity.

"Germaine Greer and fellow feminists not withstanding, I do not love what has happened to my buttocks. I would happily have foregone the experience that is supposed to make me proud of my wrinkles."

Just Me, her autobiography released last month, is a moving story about moving on. It is testament both to Sheila's survival instinct and her appreciation of life having watched the death of someone she deeply loved.

The overwhelming pain of losing John after 28 years of passionate togetherness, and to the same cancer of the oesophagus that had killed her first husband Alec Ross 31 years earlier, left her teetering on the very edge of depression.

But the indomitable Sheila, who shot to fame in Sixties sitcom The Rag Trade and has been a star of stage and screen for over 40 years since, fought back.

"I could feel myself getting depressed. I am prone to it and I knew I had to stop it from happening," she says. "I had to force myself to take risks, to live again."

Realising that she was totally alone for the first time in her life, and that her solitude gave her the freedom to do exactly as she pleased, she went travelling.

"I went off alone. It wasn't brave, it was a necessity. A sensible, practical thing to do," she explains.

"Gardening, grannying and grumbling, while they all had their pleasures, weren't going to fill the aching void that John had left.

"I had a choice. I could be a depressed widow boring the arse of everyone or get on with life.
And I've always found that a different setting, with so many wonderful or even rotten new things to go and see, takes you out of that place."

Her previous book, The Two Of Us, published in 2004 just two years after Thaw's death, was more about loss than recovery.

It was made up of three stories, running concurrently; there were hers and John's memoirs, and then the extracts taken from a diary Sheila had kept during John's illness. Sweeney and Morse fans snapped up the book, but it was the diary excerpts - frank, raw, courageous - that touched the hearts of thousands of widows and widowers.

"I was amazed at the letters I got," she says. I had no idea it was going to affect people like that," she says, explaining that the book which became a Number One best-seller and a Book Award winner only came about when a writer planning to pen John's biography asked for Sheila's assistance.

"They said that, if I didn't want to help, they would still go ahead and tell it warts and all. I didn't mind the truth being told about John. He was an alcoholic. But I didn't want that to be told in the wrong way," she explains.

"It also dawned on me that John and I had lived through an extraordinary period in social history. We had been children in the war and risen to follow our dreams from very humble upbringings, as did so many people of our era."

Cathartic though the book had been to write, however, its success threatened to paralyse her.

"Three years after John's death I was speaking about him a lot on book tours and there was an increasing danger of me becoming a professional widow," she admits.

"It took me a long time to accept that he wasn't coming back. But then I realised that episode of my life was over and I had to make a new one.

"I needed new friends and new activities to fill all the time that had previously been filled with him."

Fuelling her drive was the fact that John had been nine years younger than her.

"By rights, I should have gone first," she says. "For me to have thrown away years just crying would have been such a betrayal of the years John didn't get to have."

And so, off she went on a succession of holidays that were as much about exploring herself as a foreign clime. First came a budget flight to Italy and that lavish hotel where she discovered not only the sagginess of her derriere but also the joys of sightseeing and people-watching on her own.

Next came Budapest, where she found herself drawn to discover more about the horrors wreaked by the Hungarian Nazi Party.

Her fascination with the suffering inflicted during World War Two stemmed from her childhood in London's blitz, and was to re-emerge when she took part in the BBC programme, Who Do You Think you Are? Researchers discovered she had German ancestry, forcing her to confront her racism of the entire German race.

After that there was Thailand, where she managed to get herself arrested for entering the country illegally.

Trips to Venice and Milan proved magical, although thankfully less eventful..

And all the time, there has been her work to keep her busy, thinking, young at heart.

Sheila, an OBE, has a diverse range of talent. She has been a regular grumpy old woman on the BBC show of the same name and also had a comedy cameo in the Catherine Tate Show.

She has just finished a sell-out run of The Anniversary in Liverpool and London and is currently filming the BBC's dramatisation of Charles Dickens' Bleak House.

In 2006 she starred in Cabaret in London's West End for six months. She acted her pants off on stage, winning an Olivier award, but she says one of the best bits was the regular after-show, late-night drinking sessions with the cast.

"I did all the partying with the kids afterwards because there wasn't John to go home to.

"I hadn't really done that before and I had a wonderful time. I do enjoy the company of younger people.

"I'm so proud to say I've been made chancellor of The University of Portsmouth and being able to involve myself in the lives of the students is just brilliant.

"I think it's so important to stay open-minded and curious.

"Too many old people think they know it all. And we don't!

"You know, I hope what I've done since his death is a tribute to John; that he made me enough of a person to go out and do it," she says.

"Of course I miss him still. Of course I wish we could have been hand in hand in our old age. But that can't be.

"An awful lot of people condemn themselves to be grief-striken. Women hug widowhood around them and spend the rest of their lives in mourning.

"I think that's so sad. You're still alive; how stupid to waste the time you have."