My day as Lord Mayor of London

What's it like to be Lord Mayor of London? A few jolly japes while you wait to topple the Prime Minister? No, not that one. The other one: the ceremonial role which dates back to 1189 and involves wearing a fancy red costume. Or does it?

I've come to the City of London to find out. In fact, I'm here to be Lord Mayor for the day, or at least try to be, as preparations are made for the Lord Mayor's show. This is the annual display of pomp and pageantry that precedes the swearing-in of the new holder of the office, which runs for one year only.

By law, the ceremony must take place on the second Saturday in November. So, come rain or hail, on 10 November, Alderman Roger Gifford will travel through the City and swear his allegiance to the Queen, the 685th person to do so. It's just as well that it will be a Saturday, when London's financial district is deserted. For, as he travels from Mansion House to the Royal Courts of Justice, Alderman Gifford will be followed by 6,500 people, 125 horses, 18 cars, 20 carriages and 22 marching bands. The whole procession is three and a half miles long.

The centrepiece is the State Coach, a magnificent gilded carriage that has been used every year since 1757. It cost £1,065.0s.3d in its day, or £120,000 in modern money, which means it's older and more expensive than the coach used for coronations. Most of the time, it lives in the Museum of London, but for two weeks before the show, it goes on display in a glass box outside the Guildhall. I've come along to ride in the carriage on its journey, all 500 yards of it, to experience the regal splendour and stately bounce of this wedding cake on wheels.

Naturally, I've turned up wearing the usual mayoral garb: scarlet cloak, black stockings, court shoes and a tricorn hat. But I get a frosty reception from Pageantmaster Dominic Reid, who doesn't seem impressed. "I am not letting you ride in the carriage wearing that," he thunders. "It's disrespectful to the high office of Lord Mayor of London." "But this is real ermine!" I wail. This is an authentic Ede & Ravenscroft gown, a replica of what the Lord Mayor would wear, carefully researched by Angels: The Costumiers, Britain's leading fancy dress suppliers!

The fancy dress element is what seems to bother him. But what is the Lord Mayor's Show all about, if not dressing up? In the end, I agree to travel as a commoner: ditch the garb and off we go. Inside, the carriage is upholstered in crimson damask, and very comfortable it is too. We lurch forward, towed by a Range Rover instead of the usual six horses (only the Queen's carriage has more, with eight). The wheels are wooden with steel "tyres", but the chamber where you sit is suspended on Kevlar straps, so the ride is floaty and smooth. Passers-by gasp and point and wave. Did I really see someone doff their cap?

All too soon, our brief ride is over. Mr Reid, 51, tells me about his job. This will be his 21st Lord Mayor's Show, and his father did it before him. He shows me around the outside of the coach, decorated with paintings by the Italian artist Giovanni Battista Cipriani. Who are those pink-bottomed figures? "They're allegories of the four moral virtues of the City," he says. "Truth, Justice, Fortitude and, er, Temperance." He laughs. So he has a sense of humour, after all. Just not when it comes to dressing up in tights and saying, "Hear ye!" Clearly, that is a very serious matter indeed.