Five years and 61 periods after first trying for a baby, theatrical agent Lucy embarks upon a well-meaning but ultimately disastrous project with her emotionally constipated husband Sam, a disillusioned BBC commissioner of comedy: at the end of each new and barren day, they sit apart and compose a "letter to myself". Their alternating bulletins - charting her misery-laden attempts to get pregnant, and his unhappiness at being unable to write that hit movie - form the basis of Inconceivable, Ben Elton's latest stab at capturing the topic du jour: infertility.

As might be expected, Elton, as of August the father of twins after he and his wife conceived with the help of IVF treatment, brings huge blasts of humour to such a traumatic subject. But that's the problem. The jokes just keep coming, and damn funny they are too. Yet the result is a frequently hilarious but strangely unmoving book. Sometimes it feels like you're reading the diaries of a couple of stand-up comics, not two fleshed-out characters. No wonder they can't conceive - they're both Ben Elton!

Take out the jokes, and the sideways swipes at contemporary life, and you're left with a plot woefully short on surprises. When Lucy suddenly starts mentioning her company's latest actor, dashing Carl Phipps, you know right away that, 1,000 gags on, you're going to be presented with the evidence that Carl is not lacking in the tadpole department, and that Lucy's womb is no wrinkled prune. Similarly, when Sam secretly turns their trauma into a screenplay and plunders his wife's diary for material, wearily you sense that his longed-for hit movie is about to come.

Elton has stressed that, although it's his most personal novel to date, Inconceivable is not autobiographical. Yet, curiously, this simultaneously hilarious and tiresome book - already being made into a movie itself - tells you all about the heartbreak of infertility on Planet Elton, but much less about its effects on Planet Earth.