London to Brighton, in a museum piece

Poop poop! Parked outside the glossy red windows of the Ferrari store on Regent Street, an 1896 Salvesen is letting off steam. The stoker, for the car is coal fired, pulls a chain and two high-pitched parps cut through the background rumble of a busy shopping Saturday in central London. Fashionably logoed young men amble by gawping, camera phones extended, as John Brydon, 63, explains how this oily dogcart with a big black chimney – in Darwinian terms, the missing link between the carriage and the car – will propel itself the 60 miles to Brighton today.

"You shovel the coal into the furnace, which heats up the water, which produces steam, which powers the pistons, which connect to the crank shaft, which move the chains which propel the wheels." Simple.

Mr Brydon is one of 100 participants in the concours d'élégance that precedes the annual London to Brighton veteran car rally. The Salvesen, named after the Norwegian aristocrat who commissioned it for his estate, makes an unlikely entrant for a concours, what with the lack of any shiny brassy bits. But the crowds love it. Having never been restored, it has what a dealer might call "patina", and for the past two years has been voted the spectators' favourite.

This morning, the Salvesen, with a top speed of 10mph, will be among 500 cars setting off from Hyde Park to compete in the world's longest running motoring event. All cars must have been built no later than 1904, but unlike the Salvesen, most have petrol engines, although many with just the one cylinder. They come in all shapes, sizes and seating configurations – including the vis-à-vis, where passengers face the driver – but what is most noticeable, as heavy grey clouds brood overhead, is that the thing they mainly have in common is a lack of any kind of roof.

"We all get wet," beams Herbert Pritchard of Enfield, resplendent in a three-piece tweed suit, when I ask what happens when it rains, as is forecast for today. "Part of the fun is the challenge of getting there. There's a much greater sense of achievement if you're battling the elements as well."

Mr Pritchard is here with his entire family, including his mother and nephew and niece, and describes the event as a "big party". "It's a very social activity. This is just one of many rallies we do all year all over Europe." The route remains practically unchanged since the first rally in 1896, and is watched by more than 100,000 spectators, who line nearly every inch of the way.

There are a lot of extravagant whiskers and tweeds about, but veteran cars are not just for old men. The Bishop sisters, Emma and Elizabeth, in a 1903 Panhard Levassor, laugh off the suggestion there's anything unusual about their hobby. "Some of our best friends are in the old-car world." Like many, they are in period costume, elegant, trailing, wasp-waisted gowns with huge bustles.

Tonight, those who make it to Brighton celebrate with a black tie ball, while the drivers of the 50 or so cars that usually fall by the wayside make arrangements for the vehicles to be trailered home. Jan Haussling, over from Heidelberg in Germany, already has problems: the brakes on his 1898 Benz dramatically snapped off yesterday. But an RAC man is on hand, and promises to get them welded on by the morning. "That's the thing about these machines," says Mr Brydon. "They're living museums." Poop poop!