I seem to be missing one vital gay gene: the shopping gene. I hate shopping, dread it, fear it. Especially for clothes. My problem is that I go out with a very, very clear idea of what I'm looking for, and if I don't see that exact garment, I won't be happy and will return home with nothing. Last night, I decided I needed a shirt for Jonathan and Mark's partnership do on Saturday. I could see the shirt in my mind - a dark bluey grey, not quite charcoal, more what my mother would have called Air Force Blue. Oh, and it had to be plain, slightly shiny, and smooth, with no obvious texture. You see my problem now?

Amazingly, I almost immediately found the exact shirt at my first port of call: Selfridges. The right colour, the right texture, the right amount of shine, even the right label: DKNY. But not the right size. Smart shirts are graded by their neck size. Now, I have no idea what size my neck was, but I know one thing: it's very, very small. When the term 'pencil neck' is applied to me, it's an insult to pencils. I asked the very helpful middle-aged Vietnamese lady at Selfridges [Mrs Slo Kum?] to measure my neck, a humiliating process, made even more so when she announced: "Fourteen? Oh, I don't think we stock anything that small. The smallest we have is fifteen. If you wear this with a tie, the collar will bunch up."

Still confident that I would find the exact shirt, I headed out along Oxford Street, Regent Street, Bond Street, New Bond Street, my confidence ebbing with each pile of horrible striped, checked, embroidered, or simply not-quite-right shirts I encountered.

My other trouble is with posh shops - I fear them. I hovered outside Prada on Bond Street. On the shelves inside I could see whole stacks of shirts in my exact shade of grey. I walked past, then doubled back, surreptitiously peering into the shop, to make sure. Yes, there were hundreds of them, yes, it was a men's clothing shop, and oh God, there were four very pompous shop assistants standing round just waiting to patronise me, but what the hell, I needed that shirt. So in I went.

The uniformed man guarding the door, and no doubt springing to open it when potential customers approached, didn't bother. I rifled through the piles of shirts. They were perfect, but had no prices on the damn things. I wheeled my head around anxiously, but the four assistants stood at the far corner of the shop, gossiping snippingly, probably sniggering at the torn lining of my jacket. One of them eventually deigned to come over: "Yes? Can I help you? I doubt it very much. Are you sure you can afford these? What makes you think you can wear Prada?" OK, he didn't say that exactly, but his eyebrow did. It is perhaps fortunate that they didn't have my size, and I never did get to find out how much the shirts cost.

But this was nothing compared to my ordeal in the DKNY store, where I was tailed by a tag-team of security guards, making no effort to disguise the fact they were taking turns to spy on me, grunting into their walkie-talkies, pointing me out to each other, keeping a close eye on my rucksack.

After two hours of trudging around the West End, feeling completely dispirited, I went back to Selfridges and bought the first shirt I had seen. I know it is too damn big. If you see me tomorrow, please do not point out that the collar is bunched up. I may just hit you.