Do we ever really know our parents?

They bear us, raise us, then let us go. We grow up. They grow older. And maybe they start to need our help. But even then aren't they always mum and dad? The people with the answers. Do we ever see them as people? Do we ever see them as people like us?

Ben Watt has written a book about his mother and father. Romany and Tom. A journalist and a jazz musician. The people whom he had to help put into homes in their later years. The father who died in 2006, the mother who is suffering from dementia. "We only ever see the second half of our parents' lives - the downhill part," he writes on page one. "The golden years we have to piece together."

That is what he has attempted to do. It is a story that takes in Glasgow, post-war jazz, Richard Burton and Liz Taylor and the clown prince of British farce, Brian Rix. And, of course, it takes in Watt himself, musician, DJ, half of 1980s' indie and 90s' dance duo Everything But the Girl, with Tracey Thorn, who is also his partner.

In person - in the offices of his Buzzin Fly record label in Camden, London - Watt looks a slightly creased version of the young musician who appeared in the NME and Melody Maker way back when. He is 51 now, speaks slowly and thoughtfully and remains a skelf of a man. Perhaps that has something to do with the fact that in 1992 he was diagnosed with Churg Strauss Syndrome, an autoimmune disease that nearly killed him and resulted in the loss of most of his small intestine.

That experience led to a book too, entitled Patient. "A book I almost had to write just to get it out of my system," he says. "I was very internalised and f***** up basically by it all. I didn't have any therapy and perhaps I should have done."

People liked Patient, asked him to do another book, but it was only when his dad died in 2006 that he thought about it. He wrote 10,000 words, a "splurge of stuff" that went nowhere. But then his half-brother Roly gave him a box of souvenirs and the idea flared up again. The result is a direct, empathetic but also candid account of his mother and father's life. Two larger-than-life people. Caring and loving, but formidable. Formidable is the word Watt uses. A mother who went out to work in belted trench coats and smoked and sat at the typewriter. A father who wrote music and played piano and was funny, earthily so at times. When he wasn't withdrawn. A couple who had met when they were both already married and Romany was a mother of four. A couple who, by the time Watt was old enough to notice, were drinking too much and fighting too often.

"We're talking about 1972, 73. That was the beginning of a very difficult period for my dad," Watt says when I ask him who his parents were when he was a kid. "I think he was finally confronting the fact that his jazz career was over and at the same time my mum's career was probably never busier. She'd carved out this new life for herself as a showbiz writer, having had to shelve her dreams of being an actress. She made a great job of it. She was writing regularly for She magazine and Woman and Cosmo, interviewing film stars and coming back with signed publicity photographs and stuff. She was the breadwinner."

Watt remembers alcohol and arguments. "He was obviously threatened by my mum's success and didn't really know how to cope with it." He recalls poisonous rows bubbling up "when their lives were going at different speeds and different directions".

"I do just remember coming home from school on a Friday and thinking, 'I don't really want to be in my own house this weekend for the fear of what might kick off'. And when you are only just a teenager you should not feel like that. Fridays are the day you should look forward to. And that was so bad."

This was the worst of it. But things hadn't always been like this. Time to rewind.

Tom Watt was born in Glasgow in 1925, but he got away as soon as he could. He was playing in a group at 16, joined the Jack Chapman Band who played at the Albert Dance Hall in the city's Bath Street. He was a dapper, charismatic man who rejected his father's Christian socialism and yet inherited a similar rigid certainty of outlook about the thing he loved most, music.

What did he sound like, I wonder? Did he have a Glaswegian accent? "No," his son says. Was that deliberate? "It was typical of that generation of young men who went through the Second World War, went through National Service and the Armed Forces. It was all about social mobility. It was all about being able to change your voice to become somebody else, to shrug off this parochial, provincial voice and become someone sophisticated, to join the pilot class, to speak like Johnny Mills. When he arrived in Scarborough and bumped into Brian Rix on day one he just wanted to talk like Brian Rix. He thought, 'That is for me'."

The young Tom Watt was someone who was restless to get on with his life. As a teenager in Glasgow he met a homesick Glaswegian pianist then playing with a band led by Trinidadian clarinetist Carl Barriteau in Manchester. Tom suggested they swap jobs. For 18 months before joining the RAF he toured the country, learning how to play properly in one of the best bands in the country. He met Rix in Scarborough in 1944 when they were both called up as air cadets. It was Rix - who later would become a London West End regular with shows like Chase Me Comrade and Let Sleeping Wives Lie - who paid for Tom's first recording session in 1951. That led to a job at the BBC. Five years later he was the youngest band leader in London, on the cover of the Melody Maker, a debut album just a year off. He had arrived where he wanted to be.

His Scottishness did not make the journey with him. "I remember talking to him about the photograph my grandmother - his mother - had of him on her sideboard. He must have been 19 or something, barely recognisable as my dad. I said to him, 'Grandma says that's you'. And he said, 'No, that's who I was.'"

In our youth we are all trying to reach escape velocity. But some cords can't be cut, maybe because we don't even see them. Tom was, his son points out, as inflexible and rigid as his father in many ways. In the 1960s he was given the chance to work with George Martin and The Beatles as an arranger but turned it down. There was one last flourish in 1971 when the Dorchester hired him for a residency, but it didn't last and in many ways that was it for him as a musician. He was 45 at the time.

He just could not bring himself to bend, Watt says. "He would not be being true to himself and that mattered to him. He was a principled man." Like his own father. "Exactly. He used those rules in his own world but they were the same rules his father had in his Christian socialist world. He was very intractable in that sense. Some might say that's admirable. Some might say it's just bloody-minded. Take your pick."

His son was much more flexible. If Everything But The Girl began with jazz-inflected pop, they soon morphed through adult orientated rock to drum 'n' bass. "I think if you are interested in pop music on the one hand you are interested in technique, but on the other you are interested in concept. So you can get enthralled by the idea of a record. A country-orchestral record. A Jam & Lewis-influenced folk record. You can come up with these ideas and that can be as important as the actual ability to play your instruments properly.

"And I suppose that is where I diverted from my dad. He was all about the exploration of harmony and scales. That jazz language basically, which I think is a very male, introspective language that bubbles out in this very complex, wordless music. What you are witnessing is quite a lot of struggle, male struggle in jazz to express themselves."

Eventually, Tom gave up the struggle. For a while in the latter half of the 1970s he reinvented himself. He became a painter-decorator. Was good at it too. His wife helped, getting jobs for him from the people she interviewed. "He used to do lots of work for Billie Whitelaw up in Camden." But he was injured in a bicycle accident and he had to give up this new career. "And then it got difficult again because he became a bit more housebound."

Before her first marriage Romany had been an actress in Stratford-Upon-Avon working with John Gielgud and Robert Shaw and Peter Brook. It was her dream, but she had set it aside to be a mother and then became a journalist, flying off to Mexico to interview Burton and Taylor, asking Liz, "Whose fault is it if a marriage goes stale?"

"Well yeah, it's a big question," Watt says, when I ask him the same query. "Somebody's."

By 1983 she is writing in her diary "how I love and pity this man I have married" and believes that for her husband, "basically, life is futile ..."

By 1983 Ben Watt was in a band. He had released his first records when he was 19, gone to Hull University, met Tracey Thorn and they had become musical and life partners. The future was opening up for him, just as his father's seemed to be shutting down. The disconnect must have been clear. "Sure. I made a lot of attempts to wield it all back together. About 1985, not long after I made some money. I had bought my first flat with Tracey in north London and had bought my first car. I said to my dad, 'I'll drive you up to Scotland'. I thought it would be a great way of us coming together and him going back to his roots. It was a very mixed few days. On the one hand we had a lot of fun going up in the car but he was not in good shape. He had been drinking a lot. He was puffy and very morose and I found going up there made it worse.

"We went to visit my grandmother and I could tell he found it so difficult and didn't want to be there. He was like the little sulky teenager on holiday. It was very difficult."

It never occurred to Watt that part of the problem might have been envy. "It was only when somebody said to me recently, 'Did you ever think he might have been jealous?' That was when it dawned on me. I might have been making a success in an area that didn't interest him, but it was success. I was selling out three nights at the Albert Hall and inviting him to come and witness that. He must have had mixed feelings."

Alcohol was a crutch for Tommy, he reckons. "Partly it was a generational. Everybody drank more. And a Glaswegian thing as well. But I do think he used alcohol as an escape. It was a way of not confronting or resolving problems. He would have been the absolute perfect candidate for therapy if he had have been of a different generation and mindset. But that is probably a very similar story for a lot of people his age."

When we are young we imagine ourselves as rockets. But really we are trains. We start off as carriages, then at some point become engines and as we get older realise we are pulling carriages. Some of them are our own children. Increasingly we realise we are pulling our parents too.

The most painful parts of the book are those in which Watt writes about seeing his parents growing old and frail, when he and his stepbrothers and his stepsister Jennie become their parents' de facto carers. "It was made easier, I think, in the sense they quite willingly handed over authority to me. I remember my dad saying, 'And in all things going forward, I defer to you.' He said it quite unexpectedly one night. It was slightly passive-aggressive as well as being a handover of power. It was like, 'Okay, let's see if you can make something of this then."

There were homes. There were hospital trips. There was surgery. And then in May 2006 - two days after Watt himself was diagnosed with recurrent depressive disorder - the phone rang at 6.30am. It was Roly. Tom had died in the night in a Bristol care home.

When do we realise our parents are people too? Sometimes too late. The reason Watt has been able to write a book about his parents is because of the words and pictures they left behind for him to read and think about. Letters and posters of Romany and Tom as young and old, as lovers, as an unhappy married couple. And yes, as a happily married couple. He has memories of that too, at the end of the 1980s when they moved to Oxford, away from the drinking and the fighting. "They hauled themselves out of that moment to their credit. They shed that poisonous life."

In his mother's archive there were details he did not know. A five-year long wait for divorces (this was the 1950s), a pregnancy, an abortion. And love. There was love. There is a letter that details what Watt describes as "the awakening of my mum. She had somehow felt boxed in in her life. There she was in her thirties with four kids and hadn't really touched the sides of life yet."

Then she got close with Tom.

These days Ben Watt is a DJ, a musician, a husband and a father. He has his flaws, he knows. But we all have those.

"We're all the same in many ways," he says. "We are just trying. What I realised about my parents was that they were struggling to make sense of life throughout their lives. We all do. We're all forgivable. We f*** up, but we're forgivable."

Romany and Tom, by Ben Watt, is published by Bloomsbury, £16.99. Ben Watt will be appearing at Glasgow's Aye Write book festival on Friday April 11. See