Where Robert Harris meets Jeanette Winterson. Or not, as the case may be

I have gone down with an infection and I don't see why I should suffer alone. It isn't anything serious, just one of those acquired sensitivities to one of the many allergens of modern life. I contracted this one in my local bookshop, after browsing through the new titles section and noticing two paperback blurbs. One, for Tim Parks's novel Mimi's Ghost, read "Tarantino meets Peter Mayle" and the other, for Libby Purves's novel Casting Off, read "Joanna Trollope meets Tom Sharpe". Whether it was just the coincidence of the same locution appearing only a few shelves apart, or the transparent coat-trailing of the names selected, I haven't been able to shake this irritating turn of phrase from my mind.

In both these cases the quotations came from critics, not publishers but, inasmuch as the critics liked the books and were presumably recommending them to their readers, the difference is academic. This is criticism as the hard-sell, which can take place at any time from the moment the agent first turns up with a fresh manuscript for an editorial conference. "I think you'll find it marvellous," she says. "It's about a female composer in Nazi Germany whose muse actually turns up in person. They become lovers and transmit German secrets to the Allies, encoding them in an achingly beautiful piano sonata which Hitler orders broadcast as an example of the superiority of Aryan culture. It's sort of Robert Harris meets Jeanette Winterson." And, with any luck, when the book is published an obliging reviewer will scramble for the same cultural grid-reference (though you might have to settle for "John Le Carre meets Iris Murdoch").

Grid reference may be a little too specific, actually. This is not a precise science, more a rough guide to where in the cultural neighbourhood this new arrival is likely to locate itself, just as you might say to someone who asks where you live that it's about halfway between Bromley and Sydenham. As we orienteer through the woodland of modern commercial culture, it's helpful to have some familiar landmarks to navigate by. Some directions are more useful than others, naturally; Joanna Trollope and Tom Sharpe might at least be found in the same county, might conceivably meet at a cocktail party or a British Council tour of Pakistan - so you can vaguely see what the person who wrote the blurb might be getting at - a rather English combination of middle-class angst and sexual comedy (I guess). But in the Parks's example the way points are too widely spaced to be practical - as if you were to say to someone "turn left at Ambleside and stop before you reach Chicago". Here the promise is slightly different, of a simple money-machine alchemy; you can imagine the publisher's rep with his samples case open, trying to conjure the sound of jingling tills in the bookseller's mind. It doesn't matter that the conjunction is completely implausible; it's possible to spend a few idle hours speculating about what such a combination would look like - presumably when you call out a local artisan to wipe brain fragments off the inside of your car he turns up three days late, completely pissed, and then swans off without finishing the quarter-lights. Or you pop out in the evening for a petit rouge and get into a shooting match with the local butcher after he takes offence at your thesis that Hoss from Bonanza was obviously having sex with his horse. Even in the mind of the most fevered salesman, though, this isn't an accurate description of the book in question (a rather good black comedy with an Italian setting). It might even be counter-productive, a phrase that hopes to sell the book as hot-cakes but merely suggests that it is a mixed selection from the past-the-sell-by-date bin.

It doesn't help either that, as well as being a familiar commercial pitch, the locution is also a fairly common piece of comic architecture, in which the possibility of unlikely marriage is exploited for laughs. The writer of "Tarantino meets Peter Mayle" is clearly torn between providing a shorthand for the matter of the book, and tweaking the line into something a bit funnier than "combines witty violence with an accurate representation of provincial life". And "meets" is on hand to solve his problem, just as it is for anyone a bit short of inspiration on the day.

"Meets" is the most fashionable version of this habit of mind, one with a Hollywood briskness about it, but there are other more venerable forms - "a marriage of X and Y", say, or even "a cross between A and B". Clive Anderson offers a good example of the latter in comic mode - and of the fatal temptations of the construction. In the book accompanying his current BBC series he describes Che Guevara as "a cross between Tony Benn and Hugh Grant". This is sublimely off-the-ball, conjuring pictures of a shy, flop-haired Englishman in stained battle-fatigues. He is clutching a mug of tea and staring down from the Corderilla at the enemy forces on the plain below. "Urm, I, um... look... oh fuck, I'm shorry but we can't blow the bridge unless we vote on composite 39 first. Umm... shorry." Presumably, if there's a bit of Tony Benn in Che Guevara then the reverse is true, too, though we will have to find another half: Charles Hawtrey meets Che Guevara? Che Guevara meets Mr Pooter? Enough - I feel a sneeze coming on.