Just over a year ago, playwright Hugh Leonard received a letter addressing him as "Jack" his given name. It had been written by a stranger, the son of a girl Leonard had known years before. "I am sorry to tell you that my mother has died," it informed him. "Though the connection is one of long years past we felt at home that you would like to know about Mother's death . . . she did not speak of you very often, of course, but when she did it was with a lasting care. I remember walking with her at Carrigogunnell beneath the ruins there one lovely summer's evening . . . she said that she had a very strong sense of your presence with her there where you had walked together when you were young." The letter inspired Leonard's new play, Love in the Title, which opened last night at the Abbey Theatre. "Without it [the letter] there would be no play," says Leonard.

Carrigogunnell is a massive basalt rock on which stands the ruins of the 14th-century fortress known as O'Connell's Rock. As a young man Leonard holidayed one summer in this part of Co Limerick, where he walked out with the woman mentioned above, then a young girl. "Distance seemed to defeat our relationship."

However, the following summer he returned and the couple met up again. The play is not a conventional love story. It is about the way mothers and daughters relate uneasily to each other as people with sexual feelings. "A mother sees a daughter as a daughter, just as a daughter sees her mother as a mother." The letter started Leonard thinking, and he knew he had to return to the place.

While playwright Bernard Farrell was being interviewed for this paper last year, the phone rang. It was his friend, Hugh Leonard, apparently about to embark on a mission. "He's setting off to locate a standing stone somewhere in a field in Limerick," reported Farrell, impressed by his fellow townie's urgency. At the time, to the casual listener, overhearing the conversation, it seemed archaeology had been the motivation. Now the quest turns out to have been more personal.

Time and urbanisation have overtaken the Clough-a-Regan standing stone which now resides in the back garden of one of a row of bungalows. When Leonard and his girlfriend walked at Carrigogunnell, within two miles of it, the stone was surrounded by vast meadow. For the purposes of the play, he has returned the area to this earlier, more natural setting. Describing the stone, he offers a couple of versions of its story, adding, "it depends of course, on which you like, history or legend" before mentioning that stock character of Irish legends, Fionn Mac Cumhail. "There I was," reflects Leonard, "looking for the stone on April 1st last."

So now, almost a year later, the play written, he leads the way through his home, an apartment overlooking the sea at Dalkey's Bullock Harbour. It is a grey, dull day. The buildings, huddled conspiratorially together, are, despite the exclusive address, disappointingly ordinary looking and remain most famous for the dubious honour of sheltering the murderer Malcolm McArthur. No one could claim the complex is beautiful, but the views are wonderful.

At the mention of the death of film director Stanley Kubrick, possibly cinema's most consummate technician, Leonard looks thoughtful, shows the way into a small study, and says he was going to write about him. "It's difficult though; he was very cold." The room is small enough to warrant comment. Leonard says the lack of space influenced his decision to cull his books. "And I feel better for it. I only keep the ones I know I will reread, and he mentions a friend's widow who says the man left 700 videos. "I have about 50, how could he have kept that many?"

Gladys, the first of the four Leonard cats appears; she is also the youngest and the only female. Muscular enough to be regarded as an honorary dog, she is an unusual brindled creature with an insistent personality. "She found me," he says. The other cats are less forthcoming. One of them, PS, a beast with a fabulous plumed tail, is famously anti-social. A bizarre looking, tubby orange feline distantly related to Lewis Carroll's Cheshire cat sits on the living room window sill. The cat is not real but the Lowry over the fireplace is, as is the small Rembrandt etching.

Either loved or disliked, Hugh Leonard is widely resented and seldom attracts indifference. Much of that dislike is generated by fear; fear of his quick tongue, his memory and ready store of references. He has had more than his fair share of personal attacks and nasty mail. No one in Ireland is likely to match his specialist knowledge of vintage US cinema spanning the years 1935-1955. Rows of reference books overlook his desk, but he seldom consults them. "It's all in my head. It's sort of a hobby." Favourite movie? "On the Waterfront." Best Performance? "Brando in it - very powerful, urgent, sympathetic." Music? "Dixieland but not jazz." Food - he did write a restaurant column? "Well no, that was more of a piece about whoever happened to be my guest. I don't know enough about food to write a column on it."

Hugh Leonard may not be perfect, but he has never tolerated pretension. His candour makes him a lively, opinionated colour writer, and an able adversary. Regarded as a popular playwright and busy adapter, whose work has filled theatres rather than volumes of criticism, he has paid for this popularity. "You can write a serious play through the medium of comedy, but in Ireland comedy seems to be suspect. If it is accessible, it is deemed shallow. If your work is liked, it's a case of `if he's liked, something must be wrong; he's not boring, so he must be shallow'. " On mention of the commercial success and limited critical endorsement also afforded to Bernard Farrell, Leonard quotes Gore Vidal: "whenever a friend succeeds a part of me dies".

Leonard's success outside Ireland has included various US awards. Da not only won a Tony Award for Best Play in 1978 but it also took the Drama Desk award and the New York Critics' Circle award. Aside from Da and A Life, the Harvey Best Play award winner of 1979/80, he has also written two atmospheric and engagingly unsentimental memoirs, Home Before Night (1979) and Out After Dark (1989).

Observers queried his omission from the Field Day Anthology of Irish Writing. This doesn't bother him. "I was approached, at least my agent was. But the plan had been to represent me by the last six pages of Da. By then he's a ghost - it would be out of context and the whole thing wouldn't have made any sense. I declined to let them use that particular excerpt but suggested there was plenty of other work to choose from. There was no further contact. That's what happened. But I also think the anthology had a nationalist agenda, and I wasn't green enough for it."

A heart bypass five years ago has left him condemned to walking a couple of miles a day. He moves slowly and seems quizzical; his natural expression hovers between amused and baleful, almost patrician-like - approaching that of Vidal whom he admires. "I don't like his fiction - I find it very dense - but he is a great commentator; very funny, very smart and knows American politics so well." Leonard would probably quite like to be the Irish Vidal; Leonard is quick - but nobody's that quick. Pale blue-grey eyes scan the world from behind big glasses. In person, Leonard at 72 remains very Dublin; laconic if edgy. He talks anecdotally but is directed. Among his passions is inland waterways. He and his wife travel to France twice a year to indulge this love. "There are 5,000 miles of inland waterways in France. I tried it here. Had three boats. But the weather defeated me. Sold them. There's this boating saying, `the second happiest day of your life is the day you buy your first boat, the happiest day is the day you sell your last one.' In France at least, you can almost take the weather for granted."

Even the one-liners carry layers of meaning, as do his pauses. This new play has pleased him. At the moment it is seldom far from his mind or his conversation and, as he is quick to admit that "I have written bad plays as well as good ones", he would seem a fair judge of his own work. It is an intensely imagined piece: the three characters all inhabit different time scales; the grandmother is a girl of 20 in 1932; the mother is a married woman of 30 in 1964, while the granddaughter is a world-weary 37 in the 1990s. Leonard's daughter's reaction on reading it was interesting. "I was going to make it longer - it is only two hours - and she emailed back, `don't force it'. " She also asked if the grand-daughter was based on her. He said no, but she remains unconvinced.

Asked about his reputation for being cantankerous, he says: "I'm not . . . always. Sometimes, I admit, I do like to have a go, but I am content." The question makes him refer to Gay Byrne. Are they friends? "I never know." It is a typical Leonard comment. He describes the broadcaster as "probably the most adored individual in this island". Leonard, as resilient as he is sensitive, leaves one feeling that he is both detached observer and self-protecting inhabitant of his own world.

On the subject of reviews, he was recently told he should demand a jury rather than a reviewer. Returning to the subject of his relationship with Gay Byrne, he explains: "We both got burnt by Russell Murphy. Remember the accountant? He was supposed to invest our money. Gay Byrne lost £73,000 and I lost £258,000. It was worse for Gay because Russell Murphy had been a personal friend." Within days, Leonard, on moving some shares, discovered Murphy had forged Leonard's name for a loan Murphy had taken out. The black humour of the business still amuses Leonard more than the breach of trust hurts. On Monday he had just completed his final re-writes, and mentions that the mood and texture of this three-hander suits its director Patrick Mason very well. "It's about relationships." Having watched four previews he says the fourth performance was exactly that of the ideal first night. "It was a great audience. I'd love to kidnap it." He seems excited rather than worried. "This is one of the best plays I've done."

Meanwhile the cat is preparing to leap onto the chess set, which is ready for play. A mummy-like head shrouded in crepe bandages resides in a glass case. It looks like a death mask of sorts. "I was given that when I did The Mask of Moriarty, a Sherlock Holmes spoof. They thought I'd like it . . . It's still there."

The facts of his childhood have been well documented. Hugh Leonard is the pen-name of one Jack Keyes, born John Joseph Byrnes, but adopted by the Dalkey couple who gave him their name and a home. Being adopted is something he has come to terms with, "the jelly is set by now" he says, adding, "What's that Kirkegard said? `Life has to be lived forward but it can only be understood backwards'."

He sits silent, waiting for the next question, but then continues: "There is a lot of talk about the unborn child but not enough about the born. There are feelings of rejection," and he mentions a friend whose mother died when he was 10. "It left him with an attitude towards women of life-long hatred. It's always one or the other; you resent women or you want to understand them. Being adopted does colour your life and attitudes. I tried to track my mother down, but the closest I got was to a lodging house in North Circular Road. I was always curious, but never obsessive."

Born in November 1926, he says he was adopted when he was 10 days old. "My mother went into town to Holles Street and came home with me. She never said a word to my father; adoption was a lot easier in those days. A few years later she did the exact same thing with a dog and didn't consult my father that time either. The dog's name was Jack as well. It made for some confusion." Having written hilariously and movingly about his early years in Home Before Night, the real point is that while mention of Dalkey evokes privilege, reality for the family was harsh. "We lived in a two-room cottage in a back lane." His father worked as a gardener for the Jacobs, Quakers who lived in a big house named Enderley. The Jacobs were the closest to quality young Jack got. Mr Jacobs died, and in time his widow too. Their married daughter ensured that a small quarterly allowance was paid to Jack's father. It was duly delivered with some ritual.

Following the death of his maternal grandmother, his mother's eccentric sister joined the household. She was quite slow and as an adult woman made menacing use of her doll's pram. From the local Harold Boys' national school, he went to the Presentation Brothers on Glasthule on a scholarship. Life became more difficult there as much was made of his circumstances. "I lived in dread of being followed home." What was he like at school? "Great at English and, unusually for a writer, very good at maths." Latin was a different story and caused him to fail the Inter Cert. He repeated the year and "barely passed it". On arriving back the next September, he returned to the fourth year classroom. No one seemed to notice. He stayed. This time, at his third attempt, he came third in Ireland in the exam. "It was the least I could do," he says.

By then he had already had a job. "I was a soldier in Olivier's Henry V. I can pick myself out, drowning in a French swamp in Powerscourt. The Agincourt scenes were all shot here. We got paid £4. If you had a horse, it got £8." There was also a stint as an office boy with Columbia Pictures in Abbey Street. He had also sat a Civil Service exam which in time offered him temporary employment which he accepted. It is a point of honour that Leonard makes it clear he was an appallingly unambitious civil servant. Promotion became something to fear, should it make him stay - which he did for 14 years.

While working in the service he became involved with Lancos, its amateur dramatic society. Acting was not his strength; writing was. The group performed his Nightingale in the Branches. He left the Civil Service in 1959 and became a full-time writer.

Of the many elements which make up the contradictory character of Leonard is his relationship with his adoptive mother, who emerges as a possessive individual. "It shows in Da, I think, the character of the mother is more strained. My mother was uptight and private. Whereas my father would have loved to have been in a play, my mother wouldn't have liked that."

They had been close when he was a small boy; it was she who encouraged his interest in cinema. She found it very difficult to let go. "It probably is harder for adoptive mothers to see their children leave," he says. His father, as Leonard recalls in Home Before Night, "made it easy for me to escape . . . with my mother it was different. She was a woman of passion who let nothing and no one go from her easily." Within 10 years of writing that, time and distance had made it easier for him to express his feelings for her. "She maddens me: whenever I try to write about her, a stranger spills on the page: querulous, sharp-tongued, slow to praise, her antennae alert for an injustice or an imagined snub." It seems she spent years preparing herself for his eventual leave-taking. How did she feel about his writing? "She wasn't interested; she wasn't interested in writing. But I think she also saw it as something which would further distance us."

Leonard married in 1955. He and his wife have one daughter. In Ireland, he is larger than life. How well does he know the country? "Well. I love Belfast, Galway. I've only been to Sligo once, but when this play goes on tour, I will have been to Sligo a second time."

Of his many adaptations, the most recent of which were Dickens's Great Expectations and A Tale of Two Cities, he says, "often what I've done is think of a book I would have liked to have written and an adaptation gives you a chance to write it. As for Dickens, he's made for the stage."

He has done a lot of journalism, specialising in long feature reviews on cinema. Unlike many writers, he doesn't disparage such journeyman work. "I enjoy it. You can't write plays all the time - I can't - but I enjoy writing. You only have one good idea a year; that leaves a lot of time to do other things."

Love in the Title is at the Abbey