Serving wenches, Yeomen of the Guard and 17th-century grandes dames wander the royal apartments of Hampton Court with groups of captivated guests in tow. But this is no kitschy Historyland theme tour. The art of 'historical reinterpretation' is serious business. Photograph by Glynn Griffiths
If there is one thing guaranteed to make your palms itch with the desire to see something, it's a sign saying "No Entry". Hampton Court, still inhabited here and there by old ladies who have endeared themselves to the crown, is full of them: black gloss-painted barriers scattered liberally under arches.

Jane Malcolm-Davies, in a black wool minidress, marches past one and through a low doorway. Beyond is a magnolia-painted corridor. "This is actually part of Wolsey's apartments," she says. "It used to be a delightful Department of the Environment green." Behind the walls, early visitors are ooh-ing at the Cardinal's exquisite taste in murals. Here, at the cutting edge of heritage, is something more practical: a lift that can hold five people, as long as they've brushed their teeth. It takes us to the second floor. There are buttons for the first and third, but it can't stop at either. The exit from the first is actually bricked up.

Next to a grace-and-favour apartment, whose ornately carved entrance belonged to that unfortunate divorcee, Catharine of Aragon, we enter a series of cluttered rooms. It's like being backstage at a very well-endowed school play: bulging racks of puffed silk dresses, swords, shoes, pikes, codpieces, corsets and hose. A mantelshelf serves as a stand for a set of polystyrene heads. Each bears a frizzy perruque. Elizabeth Taylor would be licking her lips.

Half a dozen people bustle about in various states of undress. Tristan Langlois, who kicks off the first tour of the William and Mary apartments, is already frock-coated, and fiddles with his wig. Lucy Capito, who guides people through Henry VIII's state rooms a quarter of an hour later, has all but her lacing to complete. Julie Hudson and Alison Sim wear linen shifts. Roy Porter is in frilly shirtsleeves.

There's a certain air of tension today. Julie, just back from holiday, is doing her first day as a Tudor, after three-and-a-half years in the following century. She's been preparing for a couple of months. "I'm very nervous," she says. "I did all the research before I went, and when I came back I couldn't remember anything about William and Mary, which I've been doing for more than three years. And Henry VIII is a total blank now." Alison calmly expects her to be fine. "It's always like this when you step out. But you bounce off the room a lot; there's always something that will spark your imagination, or someone will ask a question that sets you off."

Roy, meanwhile, is doing his first day ever in costume. He's going to be a Yeoman of the Guard - "a Stuart Yeoman of the Guard" - and shadow Tristan. He came down from Oxford a couple of years ago ("I guess the subfusc prepared me for dressing up for a living") and worked in a warehouse before he joined JMD Heritage Interpretation. "It wasn't very enjoyable. No colour, no frills." He's got the frills now, in abundance: Jane is picking his hose. "Do you want the green or the pink?" Everyone looks. "Pink," they cry. "Definitely," says Jane. "Shows how much of a man you are."

Hampton Court has been dressing a proportion of its guides in costume since 1992. The idea was the brainchild of the Historic Royal Palaces Interpretation Manager, Anne Fletcher. "We wanted to think of a way of giving information that was fun, and to make it as interactive as possible. Theory about how people learn and retain information suggests that the more you involve people, the more they remember. If you put a sign in a room saying, "This was where the farandole was danced", they look at it and it means nothing. If you show it taking place, it's more memorable. If you let them learn the steps, it's even more so." After a successful experiment with hobby historians in the Tudor kitchens, Jane, who had co-founded the heritage interpretation company Past Pleasures in 1989, was drafted in to set up a professional team, and the rest, literally, is history.

The Malcolm-Davies guides have taken the costume thing to a new level. One could assume, glimpsing them unawares across the Clock Court, that this was some ghastly themeparking, and indeed the guides themselves refer jokingly to their patches as "Tudorland" and "William and Maryland". Actually, they're more serious than that: you need a degree at least to be part of JMD's 18-strong staff, and everyone is expected to contribute to the knowledge pool each year. Alison's book, The Tudor Housewife, is published by Sutton in September, and academic vacations see James Loxley, a lecturer at the University of Leeds, don tricorn and codpiece and swank round the royal apartments. There is very little you can ask these people that they won't be able to come up with a plausible answer to.

And the punters love them. In Tudorland, Lucy leads a group of a good hundred round the sights. They brush occasionally against another group led by a more familiar type of guide - there will always be people who will doubt the credibility of someone dressed as a serving wench. Lucy's gang is captivated by the combination of theatricality, humour and grinding knowledge, and participate eagerly.

Oddly, people seem more willing to ask questions of someone in a wimple than a badge. Maybe one feels less self-conscious about hand-waving when the person one is approaching looks so much more conspicuous.

There is also a tactile quality about these guides that you could never get from a hairdo wearing a pussycat bow. Their clothes, made in obsessively accurate detail under the auspices of the costume manager Caroline Johnson and costing around pounds 1,000 per outfit (and that's before you add the wigs and shoes), are subjected to constant assault. "A lot of people," Julie sighs as she pulls on a starched linen cap, "want to feel your corset. Particularly men." Brenda, responsible for costume maintenance, has her work cut out. "The wear and tear is enormous. A lot of the garments can come apart very easily in an afternoon. The braid on the Yeoman of the Guard costume can come in hanging off. I'll be putting them back together during the rest periods."

Apart from the manhandling, they enjoy their costumes. "My bodice," says Jane, who waltzes through the apartments dressed as a 17th-century grande dame, complete with heart shaped beauty spots, "is better than a Wonderbra. It's worth all the inconvenience. It gives me a cleavage, which I would never have in normal life." And then there's the underwear question. "Personally I find it more comfortable not to wear any knickers. You've got all these layers of petticoats and it gets very hot. Knickers were really only invented in the late 19th / early 20th century. Actually, I find that quite an interesting subject to discuss with visitors, and they do ask, you know. And about codpieces. Laundry. Personal hygiene. All these things are of great fascination to the general public. You can go from underwear to politics in one breath. It's funny the leaps you can make."

Lunchtime, back in the dressing room, and everyone dons butchers' aprons as protection. Roy has acquitted himself well, even if his perruque and flat topper did make him look like the guitarist in Guns N' Roses. James fishes a wristwatch from the flap pocket of his frock coat. Tristan is a bit battered from the personal attentions of a thousand punters. "They'll come up and start tugging wigs and grabbing clothing without asking you. They wouldn't do that with an ordinary guide. The first time it happened, I was shocked. It's this velvet suit that does it. I get far fewer people wanting to touch me in my green one."

"I know," Lucy replies. "A lot of them think we're only there for photographs and that we're no better than models. They put their arms round you and try to kiss you - particularly foreign men. They think because you're dressed as a wench that you are one."

This sounds like purgatory. They disagree. "It's a brilliant job," says Julie. "It's one of the few ones where you're encouraged to carry on learning. You're always researching, you're always reading, you're always finding out new things. That doesn't happen in most jobs." Lucy still gets a buzz from it. "I love it. It's great seeing people's fascination. They've seen the clothes in pictures, but they can't imagine how it worked in reality. It's like seeing a picture come to life."

Things can get a tad tricksy, though. They're surprised by how few adversarial point-scorers they come across, but they all get put on the spot from time to time. "This lady once asked me," Lucy recalls, "if we were in the room where Jane Eyre was executed." Old Henry, it seems, was more of a polygamist than we thought.