NOT too long ago a literary critic was able to describe Ian McEwan as "a marvellously macabre fictionalist". There was a sense that McEwan inhabited something of a niche, in which one often shocking event was examined; it usually involved people at odds with the world in a number of ways and invariably had seismic consequences. Then came the more expansive phase, including Enduring Love, Atonement and Saturday. Elements of the forensic McEwan were visible, but he had embraced character and left behind him existential angst. In the process he was acknowledged as the Crown Prince of English fiction. Critics acclaimed him, the public loved him.

His short new novel is called On Chesil Beach. Could this title be McEwan's way of thumbing his nose at those who thought his use of 'Dover Beach' in Saturday as a prophylactic against imminent violence was absurd? Chesil Beach in Dorset is the setting for the calamitous wedding night of Edward Mahew and Florence Ponting. Neither of them is sexually practised and Florence, a musician, is terrified of sex and dislikes Edward's constant attempts to push the sexual boundaries. This is l962, when, we are reminded, sex was not as freely available or as openly embraced. Larkin's lines about the suddenness of the change come to mind:

"Sexual intercourse began in l963 (Though just too late for me) Between the end of the Chatterley ban And the Beatles' first LP" This sexual mismatch leads to the absolutely disastrous wedding night - a night which is to change their lives.

McEwan is interested still, it seems, in these seminal moments in a life. He describes the regrets of the couple in these terms: "That is how the entire course of a life can be changed - by doing nothing." The moment critique in the lives of the young couple is only reached after wonderfully composed accounts of their family backgrounds, their interests and their sexual differences. Resting rather significantly in Edward's history is the fact that he used to like a good punch-up on a Saturday night, until he went to London University and discovered that that sort of thing was considered a little rustic. He is an intelligent lower-middleclass boy from an Oxfordshire village, with a brain-damaged mother, who falls in love with the beautiful musician daughter of a successful Oxford family, mother an academic, father a manufacturer.

McEwan has always been interested in class and there is a sense that Edward is riding for a fall, rather like Robbie in Atonement. This idea that the slightly lower orders are bound to be put in their place by those above them is a trope of English fiction, as Brideshead Revisited and The Line of Beauty testify. But the class Chesil Beach in Dorset is the setting for the calamitous wedding night of Edward Mahew and Florence Ponting difference is not a major theme here, merely a kind of background noise. The two households - the chaotic Mahews, living in near squalor with the secret of the mother's brain damage and the aesthetically more advanced, but emotionally more retarded, Pontings - are contrasted subtly and economically to create a familiar McEwan sense of unease.

The unease in this book is mostly sexual. The young couple are hopelessly mismatched sexually, Edward desperate to possess his new bride and Florence desperate to try to get through what she dreads most:

penetration. She blames herself for her fears. There are lots of hints from the omniscient narrator that the whole issue would have been resolved if only they had been born a little later, in the more permissive times which were to follow the next year, according to Larkin's timetable.

The awful dinner the two have to eat in the hotel before they can go to bed is wonderfully, exquisitely, painfully, described, the most evocative detail being the cherry skewered to a slice of melon.

What happens in the bedroom afterwards is truly a tragedy, brought about by what John Osborne said was the inability of the English of the period to feel.

When Edward finds a stray pubic hair as he attempts to get Florence aroused, you see McEwan at his forensic best: that lone pubic hair contains more foreboding than any pubic hair in literary history.

I can't reveal more of the plot because it hinges on this wedding night. But it is a fine book, homing in with devastating precision on a kind of Englishness McEwan understands better than any other living writer, the Englishness of deceit, evasion and regret.

With On Chesil BeachMcEwan has combined the intensity of his narrowly focused early work with his more expansive later flowering to devastating effect.