`I've never actually thought of myself as a novelist. I'm a poet who happens to use prose fiction as a sort of vehicle for my imagination." Until 1981, D. M. Thomas could, in fact, be fully described as a poet and academic, who had "a reasonable reputation, but in a small way". Then, with his third novel everything changed. In Britain The White Hotel became a critical success nominated for the Booker (losing out to Salman Rushdie's Midnight's Children) but in the US the sexually provocative account of a young woman's psychoanalysis with Sigmund Freud became a literary phenomenon, selling over one million copies. Film rights were sold years ago, but in spite of numerous treatments (including screenplays by both Thomas and Dennis Potter) the novel has yet to materialise on the screen.

Both Potter and Thomas had a very similar backgrounds, both bright working class boys from rural backwaters (Potter from the Forest of Dean between Wales and England, Thomas from Cornwall) who made good. But in 1949, when Thomas was 14, his family emigrated to Australia. Although the stay was short , (two years) it was pivotal to his future: the 28-day sea voyage gave him unfettered access to the ship's stock of books and in Melbourne he discovered poetry. Also, he says, being so far away from his roots gave him a perspective that marked him out as different from his boyhood friends in tinmining Cornwall.

Once back in England, Thomas followed the usual route for bright working class boys of the period (including Potter): national service followed by a scholarship to New College, Oxford. His time in the army coincided with the most bitter period of the Cold War, and he was selected for the Joint Services School for Linguistics where he learnt Russian. He has since translated Pushkin and Ahtmatova and in 1998 published a biography of Solzhenitysn. It was Anatoly Kuznetov's account of the massacre of Jews at Babi Yar that was the basis for the second half of The White Hotel, the starting point for the first being an erotic poem originally written for a science-fiction journal.

Using historical events as backdrop for his fiction is something D. M. Thomas has continued to do over the past 20 years. Flying Into Love (1992) was a conspiracy theory take on the Kennedy Assassination, for instance, and Pictures at An Exhibition was set in Auschwitz and concerned Mengele. Now 20 years on from his first heady success, Thomas has turned to fiction itself as his jumping off point with Charlotte, a novel that begins where Charlotte Bronte's Jane Eyre ends: with her marriage to Mr Rochester.

Jane Eyre, it transpires, is the most widely read and translated novel in the English language. Its enduring power, Thomas believes, is due to the fact that so much of it was written at a subconscious level. "Charlotte Bronte was not aware of the modern feminist interpretations of it, of the wild anarchic dimensions. But what she consciously thought of as this horrible woman in the attic, this dreadful immoral creature, in some ways did represent a side of Charlotte herself."

A reworking of Jane Eyre was a sudden impulse, Thomas explains. "My last work was a biography of Solzhenitsyn which was a total departure for me - three years of hell, almost Gulag time. I thought, I need something quite short where I can let my imagination go riot for good or ill."

Not only had Solzhenitsyn proved a professional nightmare; Thomas's wife died of cancer while he was finishing it. "I needed a diversion and somehow Jane Eyre came into my mind and the thought of how a modern woman, a woman very like Charlotte Bronte - intelligent, bright, from the provinces - would now have such a different life - love affairs and broken marriages and so on - whereas with a man there would not be such a striking difference."

Charlotte is by no means a sequel in the conventional sense: such an exercise would be "pretty pointless", Thomas says. "I always knew that after about five chapters it was going to slip into this modern figure. Although I do enjoy trying to echo a voice, I wouldn't want to do a whole book in it."

In Charlotte, as in Jean Rhys's novel revisiting Jane Eyre, Wide Sargasso Sea, the character of the mad wife re-enters the story. Barely more than a shadow in Jane Eyre, Jean Rhys's Bertha is a woman of tragic dimensions. By chance Thomas had never read Wide Sargasso Sea. Now that he has, he sees that their approach was in any event very different.

"Wide Sargasso Sea is one of those essential books that a writer writes because it relates so intimately and deeply to his or her own life and that obviously applied to Jean Rhys with her background in the Caribbean. Mine isn't a book like this at all. I wanted to show that each age has its own enslavement; we tend to think that in our age, we're enlightened, and of course it's not true. We have our own mind-set, our own imprisoning values."

One imprisoning value of our own time, he believes, is political correctness. In Charlotte he recounts how Victorian nannies would suck the penises of small boys to calm them down and send them to sleep. "This happened in puritan Victorian England. And although terrible things happen with sexual abuse with children, we seem to have gone to the opposite extreme. Nowadays a teacher can hardly put an arm around her or him without being suspended . . . "

D. M. Thomas was a teacher for 20 years, first in a grammar school in Devon and then a teacher's training college in Hereford. It was only when the college closed down that he turned to writing full-time. "My friends were getting other jobs; my best friend committed suicide. I needed to make friends. So I thought the best way of doing that is to write a novel where there are characters. So that's how I wrote my first novel. I literally made friends on the page. My third novel was The White Hotel and was a success so it came at the right time."

Thomas has published 11 novels since The White Hotel but that first success has never been repeated. Was the pressure just too much? "Everything came together in that book, luck was with me and I thought I'm not going to write another White Hotel in terms of the acclaim, so I just accepted it . . . All one can do is write genuinely and honestly and that's what I've done."

Charlotte: The Final Journey of Jane Eyre by D. M. Thomas is published by Duckworth next week.