There aren’t many literary novels with a physicist as the hero. McEwan breaks the mould in his latest book, which follows the tribulations of Michael Beard — a fat, short, bearded scientist who is irresistible to women.

His fatness, and his disgusting eating habits, are described in such detail that it is difficult to understand his attraction, and McEwan brings out the full power of his virtuoso writing to persuade us to care about his unengaging hero.

Beard’s pulling power starts at Oxford University, where he is attracted to English student Maisie. At first she dismisses him for reading such a boring subject, but he lures her by memorising passages of Milton, and offering profound comments on the poet’s life and work.

Beard reflects that it would be impossible for an English undergraduate to reverse roles in this way and understand the intensely difficult theories being wrestled with by the scientists.

McEwan has apparently done this himself, and succeeds in making the quantum mechanics and climate change science utterly convincing. Beard has patented a way of generating power using artifical photosynthesis; an idea stolen from one of his post-graduate students.

By the end of the book, our hero has gained three stone by eating crisps and nuts, ice cream, deep-fried snacks and piles of pancakes. This, and his unscrupulous womanising, seems to be a metaphor for the voracious consumption that is destroying the planet.

The plot allows McEwan plenty of comic digs at his pet hates, mainly involving intellectual laziness. A novelist pretends to explain that quantum mechanics proves that morality is relative; a postmodernist talks genetic theory to a line-up of embarrassed scientists.

There is also a deeply-felt description of what it feels like to be at the receiving end of a media witchhunt. Comic writing can easily irritate, especially when the author piles ridicule on soft targets. For me this happened during Beard’s trip to the Arctic, with an artists’ colony of ineffectual eco-warriors, where he is horrified to notice an acoustic guitar “surely awaiting its strummer and a tyrannous sing-along”.

But in the end you can forgive the occasional weak joke, because the book tackles important subjects with such high seriousness, at the same time as providing a few laughs.

Ian McEwan is at the Oxford Literary Festival on Friday, March 26. See, box office 0870 343 1001.