This unexpected exercise in literary criticism is prompted partly by the irresistible verve of the writing in Appassionata (whose bonking quotient is, in any case, fairly sparse - I said fairly). The dogged raunchiness of Polo has given way to a rediscovery of the roguish humour of Riders: the best of Appassionata is marvellously funny. Also, I can truthfully say that I witnessed some of its happenings in the making.
One of the book's highlights is a riotous description of a concert tour of Spain by the Rutminster Symphony Orchestra, whose fictional members are by some considerable distance Appassionata's true heroes and heroines. The model for this non-stop bacchanalia across the peninsula was a tour of the same country by the Royal Scottish National Orchestra in 1993: four concerts in four days in four different cities. Jilly Cooper had been invited along. So had I, to observe the orchestra at work and, er, play - and to observe Jilly observing them.
I promise you that the pace of the RSNO's touring schedule of performing, travelling and partying was every bit as near murderous as the book implies. When I got home, I took to my bed for a day and a half - and I hadn't even been playing in the concerts. But, far from affecting the orchestra's form, this punishing agenda if anything seemed to improve it. Four impressive concerts were the result, superbly conducted by Walter Weller, and including as fine a performance of Beethoven's Choral Symphony as I've heard anywhere.
Several hours after one of these adrenalin-fuelled occasions, I found myself in Jilly Cooper's company in a bar in Seville, along with a substantial section of the orchestra's Moulin Rouge contingent (as distinct from Pond Life, who were no doubt already tucked up in bed). She and I got to talking about her impressions of orchestral players compared to the casts of characters in her other books so far.
"They're very different," she told me. "I don't think they're obsessed with jumping on each other just because they're on tour. What they're really into is subterfuge. I love the story of the meal that some of them had in a really expensive restaurant, so that they could make off with all the waiters' evening coats and wear them in the concert that evening. Or the trick of how to avoid bringing more than one pair of shoes with you. During the concert you wear black socks over them."
Throughout the tour she filled up one notepad after another as she talked to virtually every member of the orchestra. ("I think they noticed me a bit to begin with, and then they went on with what they were doing anyway. It's a bit like being David Attenborough in a colony of pandas.") Her unerring ability to remember everyone's name was just one symptom of a real interest in other people - a quality that must be even rarer among the rich and famous than the rest of us (let alone among most conductors). The book's affectionate dedication "to the Royal Scottish National Orchestra because they make great music and I love them all" rings endearingly true.
What about the contents? Well, the Rutminster SO's antics may be gorgeously over the top, but as Jilly Cooper reminds us in her introduction, she writes fiction, not documentary. And she neatly captures the sense that the anarchy of an orchestra's Moulin Rouge element, while dedicated, is essentially benign. There's little if any of the ingrained yobbishness that (say) travelling rugby teams can be known to pride themselves on getting up to.
She has been careful, too, to conceal any clues to the characters' real- life counterparts, Yes, I do know who was observed, in the small hours of that legendary party in Barcelona, drinking Famous Grouse whisky out of an ashtray, and he/ she doesn't remotely resemble Dmitri, the Rutminster SO's "lyrical and lachrymose" principal cellist. The author has also used her journalistic skills to assemble a quite exceptional collection of viola jokes, including one featuring Princess Diana and a frog which is almost worth the price of the book on its own. And she says her next one is to be about opera. Hold tight.
n `Appassionata' is published by Bantam Press, pounds 16.99; an accompanying CD and tape is available on Warner Classics, pounds 9.99 and pounds 5.99