Do you know who I am?

The fiercest dress code outside a nudist club awaits those who win the coveted badge to the Royal Enclosure at Ascot.

What do Princess Anne, Joan Collins, Lady Jane Fellowes (Diana's sister), the porn star Linda Lovelace and Mr Blobby have in common? Answer: they have all been refused entrance to the Royal Enclosure at Ascot. Well, they couldn't let in just anyone, could they? In fact, there are now around 60,000 members of the exclusive circle of badge-holders, though in theory anyone may apply (in writing) for one of the limited number of passes issued each year. All you need is to know someone who has been a visitor to the Royal Enclosure for the past eight years and who is willing to support your application. Even then, the pass you receive is liable to be valid only on the Friday of the Royal meeting.

So you receive your coveted badge. Now whatever you do, don't forget to pin it to your frock. That's what Princess Anne did, and the official bouncer didn't recognise her, so out she went. (The conversation reportedly went: "But I'm the Princess Royal!" "Well you don't look like her.") If you do leave your badge at home, for goodness sake don't try to sneak in by wearing someone else's. That was Joan Collins's transgression in 1989 and they didn't let her back in for another six years.

Okay, the badge is sorted out and you're under starter's orders, but that is when the going gets tough, because darling you just haven't got a thing to wear. For nowhere on earth outside a nudist club is the dress code liable to be quite as fierce as at Ascot. For men the rules are comparatively simple: "Gentlemen will wear morning dress with top hat, or service dress." The colour is entirely up to you, as long as it is black or grey. No snazzy waistcoats and definitely no suede shoes or white socks. For women there is considerably more leeway, which only raises more problems. The rules say: "formal day dress with hat which must cover the crown of the head," but one woman's formal day dress is another man's tart's wardrobe, as Linda Lovelace discovered when her demure little see-through number was ruled transparently unacceptable. And Many Lenanton, in 1993, had what she thought to be a fashionably short skirt redefined by the Ascot clothes police as "no more than a wide belt".

The ban on jeans, however, is not what it was. You can't wear them in the Royal Enclosure, of course. Or anywhere else at Royal Ascot, but at the more relaxed Ascot meetings, jeans are now permitted in the less expensive stands. Until two years ago, even that was not allowed. "I'm delighted to see people in clean jeans," said Sir Nicholas Beaumont, clerk of the course and custodian of the dress code for a quarter of a century, "but when they started turning up with the knees falling out, people who had bothered to dress nicely were upset."

It is not simply a question, of course, of wanting to keep out the riff- raff. Quite the opposite in fact. The whole point is that having a proper dress code eliminates class distinctions. Like a school uniform, if everyone is wearing the same thing, there is nothing to distinguish royalty from commoners and we can all relax and enjoy ourselves.

It all goes back to Beau Nash, whose code of rules for formal assemblies and balls in the City of Bath were well established by the time Queen Anne ordered the building of Ascot racecourse in 1711. Nash took great delight in issuing orders to royalty. On one occasion, when the Duchess of Queensberry arrived at one of his functions wearing an apron, he promptly approached Her Grace, removed the offending garment and threw it among the waiting ladies' maids, observing that such apparel was "fit only for Abigails".

Nash himself always wore an immense cream-coloured beaver hat, which may have set the fashion for outrageous headgear at Ascot. Certainly his excuse for wearing it was considerably better than anything offered by modern-day bearers of millinery extravagances. Nash wore the hat, he said, to secure it from being stolen.

How much will it cost you, did I hear you say? Well, my dear, if you need to ask such a thing, I don't really think you're likely to make the grade, but for the record you may hire a morning suit from Moss Bros for pounds 39.95, plus another pounds 7.95 for the dress shirt and pounds 4.95 for the tie and handkerchief. The grey top hat will set you back a further pounds 12.95, making a grand total of pounds 65.80. If you are in the market for a fancy hat, however, be prepared to pay between pounds 500 and pounds 600. And that's without the dress to go with it.