There was a lesson that David Lodge took a long time to learn: "the best way to treat Catholic hang-ups about sex was through comedy".

So writes one of the most popular British comic novelists of the past half century in this memoir of his first forty years. It was Lodge's satirical take on the mores and shibboleths of religious indoctrination that helped make his name, yet as his autobiography reveals, he was astonishingly dutiful to his faith for many years after the cracks began to show.

He and his long-time girlfriend Mary, whom he met in his first week as a student at University College London, were scrupulously celibate until they finally married, seven or more years later. Nor was there anything unusual in this. Lodge tells us, with a flatness of tone and banality that mark much of this work, that once they were engaged, Mary working as a teacher and he as an aspiring academic and writer, at the end of the day "I would often pop round on the Vespa for a cocoa and a cuddle". It is not the stuff of the angry young men - Orton, Amis, Osborne and Sillitoe - who were making their name on the dramatic and literary scene at this time, but it was real life, as experienced by those who had been told that extra marital sex was a mortal sin.

One criticism of this book has been that there is not much sex in it, but the opposite is true. It is suffused with sexual desire, albeit much of it frustrated and repressed. During his miserable years of National Service - "like serving a prison sentence for a crime I did not commit" - Lodge requested a transfer to the Far East, which was turned down. Nothing if not honest, he says: "Perhaps at the very back of my mind, scarcely acknowledged, was a Graham Greenish fantasy that I might lose my virginity in a Hong Kong brothel, and be quickly shriven by a regimental chaplain, without real disloyalty to Mary." His interest in sex and chafing at chasteness carried an additional pressure: "the urge is of course a normal condition of youth," he writes, "but in my case it was reinforced by the belief that sexual experience was necessary to become a writer of fiction." Later, when describing his honeymoon, Lodge brings a matter of fact eye to a virginal coupling and its awkwardness, but also reflects on the pleasures of slow-flowering erotic discovery over the course of married life. Not everything about deferred gratification was bad.

The humour to be found in sex is a thread that runs through almost all his work, from his debut, The Picturegoers in 1960, to Therapy and Deaf Sentence, autumnal novels where the comedy is more muted but his voice remains in key. There is much more to Lodge than this theme, however, and one of the most interesting parts of this work is where one learns the ways in which his life and reading informed his fiction. James Joyce and Graham Greene were crucial early influences on his writing - so too Jerome K Jerome and radio comedy shows - but another was his unmarried aunt Eileen. Of all the relatives who surrounded him in early life, she stands out as a character with a rich inner life.

The only child of a professional musician, whose father played in cinema bands and nightclubs, and a mother who ran around them both like a skivvy, Lodge was born in suburban London, a place he evokes with a tender, painterly hand. Happily brought up, apart from a very brief period in a boarding school during the war, and unaware of the tensions in his parents' life, part of which was the result of a late miscarriage of a daughter in 1939, he shows himself to be a kindly, sensitive, self-centred young man, who lacked confidence but was not without determination or grit.

Outlining his upbringing with more thoroughness than it strictly requires, Lodge offers a glimpse of social history as well as his own. His time at a Catholic academy under the instruction of the infamous Christian Brothers - where as a day pupil the worst he faced was corporal punishment - and his undergraduate years (the least engaging episode in this curriculum vitae) read more like an assiduous record than memory transformed by passage through a novelist's mind, let alone one with a strong satirical streak. Only rarely does he offer an image to match the verve of his novels. One such is his first experience of the confessional, the priest "behind a grille that resembled the door of a meat safe ". Another is hearing the poet Christopher Logue read, " the phrases lingering in the air like perfectly formed smoke rings".

Methodically carrying the reader through a series of not particularly fascinating holidays with his girlfriend and chums, he eventually finds an academic post. A lucky one-year lectureship at the University of Birmingham was the hinge on which his life turned, a place where he would spend the rest of his career, making formative friendships with the likes of Malcolm Bradbury and Richard Hoggart.

At this point, Lodge's aspirations as a writer and an academic took off, leaving Mary to take care of two daughters ("Vatican Roulette" was their contraception of choice). Then, close to the end of the book, they have a son Christopher, who has Down's Syndrome.

Christopher's birth changed Lodge profoundly, his Catholic faith cast into doubt, so too his unthinking optimism. The repercussions of what was initially felt as a calamity presumably found their fullest expression in the years beyond the scope of this work, but within a few months of Christopher's arrival, one can see clear signs of the direction in which Lodge is heading, as a thinker and writer, and father.

Quite a good time to be born, whose interest occasionally flickers, but never dies, is reminiscent of his hurriedly written PhD thesis, which ran to 180,000 words. Ruefully recalling this tombstone, Lodge quotes Pascal's famous comment: "I apologise that my letter is so long; I lacked the time to make it shorter." One wonders if the same might be true of this memoir. Even so, one looks forward to the final volume, covering the second half of his life, which he tells us he hopes to write "in added extra time".