BRIEF ENCOUNTERS; He is back on our screens as Kavanagh QC, but this time heartbreaking tragedy lurks beneath the brusque counsel's courtroom exchanges. John Thaw tells Thomas Quinn how life very nearly imitated art.

When John Thaw dons wig and robes again as the gritty brief Kavanagh QC, his courtroom battles will be masking an inner turmoil.

In this new six-part series of the thoughtful legal drama, which returns to our screens this week, Kavanagh is now a widower. The workaholic barrister's wife Lizzie - played in previous episodes by Lisa Harrow - has lost her battle against breast cancer, leaving him alone but for his two grown- up children.

It's a tragedy that, thankfully, is not reflected in the 56-year-old's personal life - although at one time it so nearly could have been.

In 1988 John's wife, the actress Sheila Hancock, discovered she had breast cancer. The diagnosis brought problems in their marriage to a crisis point, and Sheila walked out on him saying that she needed time to come to terms with her illness. Six months later they were back together.

"I learnt to be more tolerant and aware of other people's needs," says John of that time. "It made me less self-absorbed and more concerned about Sheila's well-being. But Sheila and I are as happy as when we were first married, though we're obviously very different people now."

And Sheila agrees that her decision to walk out saved and strengthened their marriage.

"John and I have always had a very obsessive relationship," she has said. "But the separation made us both less reliant on each other and stopped us constantly clawing at each other. We both know we can survive on our own, which seems healthier somehow. Sadly, I came out the villain. But our marriage was going through a dodgy period. John had his problems and I needed to be alone."

Proof that they resolved their problems, if any is needed, is that the couple are preparing to celebrate their silver wedding anniversary. And their daughters Melanie, 32, Abigail, 30, and Joanna, 23, have been drafted in to help plan something special.

"I'll be relying pretty heavily on the girls to help me out but something extra special will be expected," says John. "I like the idea of having been married for 25 years. I like that comfort and security."

The marriage was second time around for both John and Sheila.

John, who was divorced from his first wife Sally Alexander, first met Sheila, who is nine years his senior, when he appeared as her stage lover in a play called So What About Love? in the late '60s. At the time Sheila was married to actor Alec Ross.

After Alec's death from cancer in 1971, John asked Sheila out to dinner. Sheila had been largely unimpressed by John the first time they met. "I could see he was very sexy and all that," she recalled. "But when I first met him he didn't look up and he was monosyllabic."

Once they dated, however, the relationship grew quickly. There was a strong sexual attraction between them which made them forget the difference in their ages.

They did have a great deal in common - both were ambitious and working class. And both were struggling to get a break in an industry that had traditionally looked down on anyone lacking an upper-class accent.

When they decided to formally tie the knot, in an era when the establishment was increasingly going out of fashion, it was partly for the sake of their children. Sheila was already pregnant with the one daughter they had together, Joanna, when they wed.

When they eventually married on Christmas Eve 1973, they did their best to keep the nuptials secret. But as they were driving home from their register office ceremony in Cirencester, they heard the news being announced on their car radio.

Following reports of their temporary separation in 1988, the couple's disputes have tended to make the headlines. Three years ago there were widespread rumours that their marriage was over when John bought a flat in London.

Friends who spoke to the media at the time told of the pair spending increasing amounts of time apart, of John's almost compulsive need to keep working and the strain it was putting on their relationship, and of Sheila's jealousy at her husband's success as Inspector Morse.

Sheila's career, meanwhile, had passed its peak - her age proving a problem with casting directors who preferred younger actresses in lead roles.

Yet despite the public interest in their private lives, both maintained a determined and dignified silence in the face of such gossip and speculation. And they were uncomfortable when the media spotlight fell on Thaw's father, also called John, last year when he was reported to be dying from lung cancer.

Sadly, his father died last autumn, aged 78, while John was filming this latest series of Kavanagh QC. It was a particularly traumatic time for the actor. John's mother had left home when he was six, so he and his father were especially close.

"I used to talk to my dad on the phone every day," says John, giving a rare glimpse into his private life. "He was a good man and I was very proud of him."

Far happier talking about his work than his family, John confesses that he'd like to give up TV - for a while at least.

"In two or three years I'd like to do a lot more theatre and put television on the back-burner. I enjoyed my time at the RSC, though I didn't like being away from home. I think I could cope with that better now.

"I'm very lucky because I can pick and choose the kind of roles I do. I'd rather like to take things easier in the future, but I don't see myself retiring completely - not ever."

The workaholic actor who has hardly been off our screens in recent years - whether it's as Morse, Kavanagh, or Regan in old re-runs of The Sweeney, and not forgetting the flop drama A Year In Provence - actually took a much needed three-month holiday last year.

"I was so tired I found it difficult to go home at night and learn my lines for the following day," he recalls. "I'd say them over and over to myself until they'd sink in - but it was taking longer and longer."

John has also announced that he is quitting Morse after 13 years of playing the Oxford sleuth. Though there is speculation that one more episode is in the pipeline, this time possibly without his sidekick Sgt Lewis, played by Kevin Whately. But fans of the acerbic, Jaguar-driving Morse should not hold their breath until the ink is dry on the deal.

"I'm getting past retirement age for a copper," insists John. "There's a detective on German TV called Inspector Derrick and the same actor has been playing the part for something like 27 years. He must be in his seventies and he's always filmed sitting behind a desk or in a car. He's too old to move about much. I don't want to be like that - here comes Inspector Morse and his Zimmer frame."

Even when John does finally leave Morse behind, one passion that he shares with possibly his greatest character creation will remain - a love of classical music.

"Listening to Bach and Mozart helps me forget all my worries," he says. "That's not to say I don't like pop music, but classical music is my way of unwinding."

When he does get time to relax, John prefers to spend time with his family in one of their three homes. They have a London residence, a Wiltshire manor house and a home in Provence. And John is at his happiest in his off-screen role as a grandad, entertaining his daughter Melanie's three- year-old son, Jack. He loves having another man about the house.

"Instinctively you react differently to fellow males - don't ask me why," he laughs.

"It isn't very politically correct but I see both my daughter and Sheila do it. You're more rumbustious with a boy."