At around 11 o'clock on Wednesday morning, that hot, dry, blossom-blowy morning of innocence and 100 per cent tax relief on pension contributions before the Chancellor's Budget statement, the post flopped through my letterbox. And among the many enticing discount curry offers and imprecations to change my telephone supplier to one who will give me free texts and fairy cakes was a stiff blue envelope.

Inside it was a stiff blue card with a sexy, mirrored panel in the middle and embossed metallic writing all around it, inviting me to “The Conservative Party Summer Fundraiser”. Enclosed was a note from the chairman (of the party, not the Party - although I'll get on to the Chairman of the Party later) saying: “Dearest Giles, Not sure if this is your thing - but would love you to come. Much love, Kate.”

And I thought: “Oh, Kate. Kate, Kate, Kate, Kate, Kate, Kate, Kate. ‘My sort of thing'? A Tory fundraiser? Are you nuts?”

I have been a Labour supporter all my life. Initially, when I was little, because Labour was in government, and I was far too cowed by authority and strong parenting to conceive of supporting anything so anarchically monikered as “the Opposition”; then, going into my teens, because my parents were staunchly Thatcherite, and I was beginning to define myself, at last, by a rejection of their values; and then, as a student, because I had come of age politically, decided I was a Marxist literary critic and thus a Marxist everything else, and so was all for social inclusion, redistribution of wealth by punitive taxation, and the abolition of the private school system that I had just left (the politics of “pulling the rope up after you”); then, in my twenties, because I worked for The Times, and The Times was Tory, and it was fun to be the only Trot on the block; and then, in my thirties, doing telly and starting to make some real money, because new Labour promised not to tax me too heavily, and I could be all bien-pensant and organic lamb chops and cool with gay people and tearfully respectful of the nursing profession, and still have loads of money and a big house and several cars.

So what in the world could I possibly want with the Conservative Party? I am a Labour man, pal. Labour till I die.

And then, on Wednesday, there was the Budget. I will lose all of my personal allowances. I will pay tax on a fair whack of my income at 50 per cent (and 61 per cent on bits of it, according to some articles I didn't really understand). And, worst of all, I won't be able to squirrel away huge chunks into a private pension so as dramatically to reduce my tax liability.

When I heard this, I immediately had two thoughts. And I will be bone-dry honest with you, where most wouldn't be, about what they were.

My first thought was: “God, I'd better call my accountant and find out how we're going to dodge this.” And my second thought was: “Hell, I'd better vote Tory.” That's all it took. That is the man that I am. That is the self-regarding, money-crazed, club-class-travelling, burglar-shooting, get-off-moi-land, smooth-palmed, island of a human being I truly turn out to be. And it makes me sick.

All my life I have believed in squeezing the rich till the pips squeak. I just never imagined that by the time they finally got round to it for the first time in my wage-earning life, I myself would be rich. And I'm furious.

It turns out that as long as I have money, I don't care about anything. I am like Fagin, hunched over his box of stolen trinkets. I am Gollum, snivelling in my lair, ogling the performance of my SIPP online, clutching the little slips that entitle me to 100 per cent tax relief on my pension contributions, turning them over in my bony fingers every April and muttering “my precious”.

By 3pm on that Wednesday - having been unable to get through to my accountant on account of his phone lines being plugged with a hundred Gollums panting for reassurance and cunning stratagems - it had dawned on me that by the time I get around to having children, and they get around to growing up, I might not, after all, be able to send them to private schools.

Except that I have always planned to educate them at state schools anyway, regardless of cost. It has been the bedrock of my revolutionary Weltanschauung. I have sworn since my own public school days that I didn't want my children to grow up into sneering, irrelevant fops like me, bilingual in Latin and Greek but incapable of hot-wiring a car. I wanted them to be normal. To do carpentry, smoke Royals, have mixed-race friendship groups and get pregnant at 12.

But now that it seems I mightn't be able to afford to educate them privately, suddenly it feels like a right of which I am being deprived. And when your rights start to loom larger in your mind than your duties, well, that's when you have become a Tory. Getting that across to the electorate is the trick, I now realise, that Margaret Thatcher and Keith Joseph pulled in 1979.

And so for the past couple of days I have been asking myself, how bad would it be to be a Tory? I have met David Cameron a couple of times. He's a charming fellow. He's really far more like me than any politician I have ever met. But do I want the country to be run by someone quite a lot like me? It's a terrifying thought. I suppose that George Osborne will run the place, really. But he's not that different from me either. Younger, and quite a lot more serious about things - but essentially just a London public schoolboy who went to Oxford and can't change a spark plug.

I did Any Questions on Radio 4 last week. I bombed pretty badly because I don't know anything about anything, but I had a lovely three-hour car ride back to London with the Tory party chairman, Eric Pickles. We turn out to have a shared love of westerns, except that Pickles has real depth of knowledge as well. And a bit of northern soul, too. A big, decent, modest sort of a man, with real hinterland. Whereas Caroline Flint, the Labour minister on the panel, seemed little more than a malfunctioning fembot. Asked tricky questions, she betrays an involuntary eye twitch, and I swear you hear a buzzing noise as the circuitry on her motherboard overloads.

By Friday, my mind was turning back to the Conservative Party Summer Fundraiser. I called an old pal, my soi-disant brother-in-law (we Tories say thing like “soi-disant”), and said: “It's two and a half grand for a table, what do you reckon? Is it OK to give money to the Tory party?” And he said: “I don't know what you mean, Giley. I've been a donor for years, ever since the countryside march. Not that I'd want anyone to know.”

He says he's up for the party, and free on June 17. So just now I went out to the recycling bin and dug out the stiff, blue card, with its sexy silver panel. And it's sitting by my computer now, winking in the sun. A cheeky, seductive wink.

I don't know. Maybe it would be fun.

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