The thing is, whenever television adapts a well-loved book, all sorts of self-appointed experts on 19th-century manners, uniforms, corsetry, accents, and “what the author really meant” come out of the woodwork.

I’m as bad as anyone else in that respect - when it’s not my own adaptation - and the strength of the feelings aroused is really a tribute to the power of the original to grip our minds and move our hearts.

In truth, we all have our own Middlemarch, our own Wuthering Heights, our own Jane Eyre, and nobody else’s adaptation is ever going to be quite right for us.

You don’t have to be a Jacques Derrida to realise that every reading is an adaptation of a kind, and that there are as many Vanity Fairs as there are readers of Vanity Fair, some differing only in tiny details from their neighbours, others contrasting so violently that they seem like another kind of book entirely.

When we look again at the film of Tom Jones, with Albert Finney’s memorably life-loving performance, we think how true to its time it was - not Fielding’s time, but the mid-1960s, when it was made. And no doubt 10 years from now, our brand-new Vanity Fair will look terribly, even comically, late Nineties, despite retaining some indelible bits of Thackeray DNA common to all Vanity Fair adaptations.

That’s fine - it’s impossible to avoid being of one’s own time, and indeed it would be wrong to offer a Vanity Fair that did not speak to our lives today. Both consciously and unconsciously, the writer, director and actors will emphasise those aspects of the book that speak most strongly to our own times. The aspects I’ve been most conscious of are Thackeray’s worldly cynicism, coupled with an odd sort of tenderness, his refusal to idolise or to countenance “heroic” behaviour in his characters, and, if I have got it right, his lack of a consistent moral stance.

So he indulges his characters for a while, then turns against them in a fit of savage revulsion, then offers them the possibility of redemption, then undercuts that with more cynicism. And Becky Sharp, an adventuress in an amoral world, has many distant relations in the game shows and gossip columns of today. It seems like a good time to let her loose again.

“But I say, come on, Davies” (says teacher Jones, throwing down his TES in disgust - no jobs for Jones again this week). “We are talking about a Timeless Classic here, are we not? Let’s not drag it through the mire with facile twaddle about Tara Palmer-Tomkinson and the like!” (Are there still any teachers like Jones lurking about in state school staffrooms - I sincerely hope so.) “Jones”, I reply, “the very point of a Timeless Classic is that it speaks in different ways to different generations, and perhaps the O-level notes you copied down in 1959, themselves copied by old Pargeter in 1934 from a set of lectures which his tutor had sat through in 1911, may not be the absolute last word on Vanity Fair.” “Davies”, says Jones, “you are an intellectual spiv, and besides, methinks you protest too much.”

Well, maybe. But there are two things that make me feel pretty good about making a living from adapting the classics (besides the money, and the delight of spending so much time in the company of Austen and Thackeray).

One is the knowledge that it encourages people to buy and read the books,in huge numbers, and a lot of those people would never have thought of doing so had it not been for the adaptations.

The other is that I know that students and teachers of English are grateful to use the television version, not as a substitute for reading the books, but as an enrichment and a challenge.

At least, I hope that’s how they use them - I like to think of students saying: “That’s not how I’d have done the opening scene - I’ve got a much better idea.” After all, someone’s going to be adapting Vanity Fair for the audience of 2010, and it won’t be me.

Andrew Davies writes for television. His six-part adaptation of Thackeray’s “Vanity Fair” began on BBC1 last Sunday. His past work includes “Pride and Prejudice” and “Middlemarch”. Adaptations of “Northanger Abbey” and “Wives and Daughters” are in the pipeline as well as a cinema film of “Daniel Deronda. ”