Michael Holroyd got an advance of £25 for his first biography in 1964, about an obscure man of letters named Hugh Kingsmill. For his four-volume biography of George Bernard Shaw, which was completed in 1991, he got an advance of £625,000, a sum which attracted many headlines.
"It was a sum that was paid over 12 years," explains Holroyd. "I've just been paid the last of it. I looked on it as a sort of middle-aged pension."
Between these two projects were biographies on Lytton Strachey and Augustus John, each of which were well-praised, although it is the Shaw quartet which really compounded Holroyd's reputation. Holroyd has the hunter's gene for what makes people tick, which marks out all biographers. He attempts, for instance, to turn the conversation round and interview this reporter instead.
Between the notebook temporarily going down on the table and the glass of water being lifted, a moment where no notes are being taken, he's in with a question himself that subtly redirects the interview. Reporters are usually adept at swiftly side-stepping such unnecessary diversions, but Holroyd makes a remarkably skilful hijacker.
The four biographies to date have all been about men. Is it easier as a biographer, since he is a man himself, to explore and empathise with his own sex? "Men are on the title pages of my books, but women fill many of the pages. It's difficult to find a good woman who hasn't been written to death."
The Strachey biography, which came out in the late 1960s, proved to be controversial. "People were appalled to read that he was homosexual. It sounds strange now but, at the time when homosexuality was still a crime, it was quite extraordinarily controversial. I felt like an archaeologist, raising this piece of Strachey's past to light again."
Holroyd is curiously vague about why he chose Kingsmill as a subject. The others, Strachey, John and Shaw, are all much better known. "I picked Kingsmill up in a public library by accident. It's true to say that nobody had heard of him before my book, and nothing has been heard of him since." He laughs. "As for the other three men - they were all bearded!"
When he's stopped laughing, he says: "My subjects are the professors I never had. They were my teachers in a way; a maverick crew."
He points out that nobody had written a weighty biography of Shaw prior to his book, and that he had had access to letters and diaries which hadn't been used before: the raw material which all biographers adore. "There were things in my life similar to Shaw - he didn't go to university, and his parents were divorced, for example. I wanted to make him a radical again, not some playwright whose plays were matinee pieces. It's all passion between the lines with Shaw."
What makes a good biographer? "It's as difficult to write a good life as it is to live one," he says after a while. "When you're a biographer, you're like a traveller going to a foreign land. It's time travel - a bit like being a science-fiction writer. You have to go back in time to find the person and then resurrect them on the page. If you can do that, if you can retrieve something from death, then you're getting there."
It's difficult to gauge whether his next comment is tongue in cheek or not, delivered as it is with gravitas: "You pay the dead a compliment by keeping them in employment."
He starts his research by reading everything on the subject. Then he writes to all the manuscript libraries where work by the subject is held. He makes trips there if the material merits it - otherwise, he gets photocopies.
He always goes to places which were important to the subject. For his Shaw research, he lived in Rathmines for two years, not far from Synge Street.
Then he arranges his material and ideas under headings. "And then I start writing - always too soon."
Holroyd thinks that the genre of biography is one which will change quite radically from its traditional format of following the subject from cradle to grave; he believes it will reinvent itself, much as travel writing did in the 1980s. He points to poet and journalist Blake Morrison's award-winning book about his family, When Did You last See Your Father?, as an example of a new kind of biographical writing.
"I think people will focus on fragments of their subject's lives, and explore those closely, such as relationships, while leaving out a lot of other things."
In an early chapter of his new book, Basil Street Blues: A Family Story, which is about his own family, he observes: "This is what has attracted me to biography: the idea of an intimacy between strangers." Later in the book, he muses: "My purpose has been to pare back a little the cuticle of time and to apply the research methods I have learnt as a biographer to my own life for a while, letting the detective work show through the narrative at some places for those who have a similar curiosity in human nature and its reworkings on a family chronicle."
Holroyd is married to novelist Margaret Drabble. He writes at the top of the house in which they live in west London and she writes in the bottom, and never the twain do meet. "Maggie and I never show each other our work. We're supportive but not interventionist. Sometimes, we discuss our work when it's at the proof stage, but not while we're writing.
"She writes contemporary novels, and she's asking the question, where are we now? Whereas, I'm asking, how did we get here?"
Holroyd thinks that his family's story in Basil Street Blues is everyone's story in ways. The book has only recently been published, but he has already had a lot of letters from people saying that they recognised characters from their own families in it.
"I think it's a book about the hidden history of families," he says. "I'm surprised and encouraged by the letters I've had in response."
He would like his next biography to be about a woman. "I'm very fascinated by a woman who modelled for Rodin." He has seen the marble sculpture. Almost nothing is known about her, other than that her lover commissioned Rodin to portray her, but when he saw the finished piece, their relationship ended.
"She's an obscure figure, just like Hugh Kingsmill. So, I'll probably be ending my biographical career as I started it, exploring the life of a forgotten character."
Basil Street Blues by Michael Holroyd is published by Little Brown at £17.50.