The noise is fantastic. Across the vast acreage of the Goodwood racing circuit, from grandstand to aerodrome, the air is filled with what sounds like a thousand screeching banshees fighting off waves of vicious giant hornets. The wail of revving engines and squealing tyres penetrates every corner of the 77th Members’ Meeting on this bright Saturday afternoon. It’s the soundtrack to a multitude of local car fanatics who are taking lunch in the Great Hall, a kind of baronial refectory, its long tables, wooden pews and tall candelabra all suggesting a medieval banqueting tent. It’s the background music to all the drivers, mechanics and technicians who throng the paddocks, readying the cars for their hurtling, breakneck circumfluence of the track. And in the Governors’ Enclosure, a kind of prefabricated Pall Mall gentlemen’s club, all wood panelling and leather armchairs, the noise almost drowns out the words and sartorial opinions of Charles, Earl of March and Kinrara, and Lord William Gordon-Lennox.

“One of the coolest things about growing up here is getting to meet some incredible racing drivers walking through the paddocks,” says Charles. “To see Emanuele Pirro, Derek Bell and Mark Webber just hanging out enjoying themselves is an incredible thing. We’ve been so lucky growing up around those kinds of people.”

“It was great to walk into the library after supper last night and run into David Coulthard, who was pouring glasses of his new brand of scotch for the other guests,” says William.

Charlie and Will, as they’re better known, are the eldest sons of Charles, 11th Duke of Richmond, whose family has owned Goodwood since 1697. The family has a top pedigree in automotive as well as aristocratic circles. The racing circuit was set up by the Duke’s car-mad grandfather, Freddie, the 9th Duke, in 1948. It became famous for its trophy races – Sir Stirling Moss, Mr Mike Hawthorn and Mr Graham Hill all zoomed around its track – but the Duke closed it in 1966, alarmed by the dangerous speed of modern racing cars. Charles, the current incumbent, a gallopingly successful entrepreneur, launched the Festival of Speed in 1993. It’s a weekend event held every July, attended by the gods and titans of Petroland.

The two boys are reliably visible figures at both the racetrack and in the stands during the horse-racing season when Glorious Goodwood, a highlight of the flat racing season, runs in July and August, and not just because they’re young milords. They’re two of the country’s most eligible bachelors. Along with their twin siblings, Lord Freddie and Lady Eloise Gordon-Lennox, they feature regularly in the society pages of glossy magazines. Today, they’re rocking a clothing line with a pretty spectacular pedigree of its own.

Connolly Leather started making upholstery for British cars in 1878. You’d be hard pushed to find a vintage Bentley, Daimler, Rolls-Royce, Jaguar or Aston Martin that didn’t feature the company’s famously supple skin. Later, Connolly Leather featured in the fittings on Concorde and the QE2. It received a Royal Warrant and became “Leather Tanners and Curriers to Queen Elizabeth II”. The company was bought in 1999 by Mr Joseph Ettedgui, of the Joseph fashion boutique, and is now run by his widow, Isabel, from a five-storey townhouse in Mayfair, London. Recently, Connolly and Goodwood got together. The former has brought out a new collection, the Driver range, inspired by the latter’s motoring past. It’s a stylish, self-consciously retro array of clothing and accessories with motor connections, partly inspired by the 9th Duke. The colours of his Gordon tartan, for instance, have been “re-appropriated” for a new cashmere scarf.

“There’s a nice match-up between Connolly’s history of working in cars and Goodwood’s authentic heritage,” says Charlie. “Everything in the Driver collection is about the culture and history of motorsport. These overalls” – he gestures at his unzipped onesie – “are probably the best example. They’ve got tabs around the ankles, so the material doesn’t drag on the floor while you’re driving, and turned-back cuffs, so you can look at your watch without having to take your hands off the wheel.” And under the overalls? “A thin, cream-coloured jumper made from super-fine merino wool, with the Goodwood logo on the collar.”

William, at 22, is the younger of the brothers by two years, and is also the taller – tall enough to carry off a pillar-box-red jumper without looking apoplectic. “I love these thick knits,” he says. “They have some Hornet jumpers that are really cool.” He shows me one in yellow-black stripes, another in rust and dark grey. “They’re fishermen’s jumpers in Shetland wool, rough to touch, thick and itchy, but on the inside they’re lined with cashmere and soft to wear.”

Will’s lower half today is encased in blue velvet corduroy – very suitable for a lord, since corduroy means “string of kings”. Is he a fan? “I just love it,” he says. “It’s so quintessentially British.”

I tell the boys I’d expected to see more leather in a contemporary driver’s wardrobe. “No, no,” says Charlie, the more forthright of the pair. “Leather is for bikers. The old racing drivers wore thick wool under fireproof overalls. That was all they worked in and raced in. It makes sense. You can’t fall off a car, obviously, so you don’t have to worry about skidding. Only fire.”

“And crashing,” adds Will.

“Fire and crashing,” concedes Charlie. “And skidding on grease.”

Charlie started driving at 12 and competed in his first race at 15, before deciding to focus on schoolwork and university. He studied theology at Oxford and now works in artificial intelligence in London. He enters “just the occasional amateur race for fun”. This afternoon, he is competing for the Gerry Marshall Trophy in a Triumph Dolomite Sprint, a 1970s saloon. How fast will he be going? “We don’t have speedos in our cars, but we have rev counters, so you can guess,” he says. “It’ll be about 120-odd miles an hour.” Is that the fastest he’s ever driven?” He gives me a pitying look. “I once did 200mph in a dragster at Bonneville.”

Will, by contrast, has never got into car racing, “though I’m happy to wander around and inspect the beauty of the cars and learn about them. But I never got my racing licence. I’m more keen on horses.” Riding them? “No, strictly gambling.”

Does he bet inadvisable amounts of money? “We bet quite carefully, Charlie and I,” he says. “The two of us share a betting account and follow a rigid point system so that, no matter how confident you are, you never bet more than two or three points on one horse.” Wouldn’t he match his car-racing brother if he rode horses? “Actually, I can’t,” says Will, smiling. “I’m allergic to horses. Really, it’s true. My throat just closes up. I need steroid injections and nasal sprays to go anywhere near a horse.” He is just coming to the end of his student life at Edinburgh, where his dissertation is on death, grief and suffering in the work of Mr CS Lewis. “Yeah, pretty uplifting stuff,” says Will. How did both brothers come to study theology? Were they believers? “I’m not very religious,” says Charlie. “But we studied things at opposite ends of the subject. I spent my time on Islamic secularism, and Will studied Christianity and the afterlife.”

What’s the most important item of clothing when you’re doing 120mph around the circuit? “The only thing you need to worry about is your shoes,” says Charlie. “Because you need to feel the pedals really well. The shoes in the Connolly range [he’s wearing brown suede ones] are great because they have a thin sole, so you have a lot of control over how your feet move. Whereas if you’re wearing trainers or thick leather shoes, you can’t feel the pedals. There’s the question of weight as well. If you’re wearing heavy shoes, you’re going to slow the car down.” But surely, a pair of leather shoes weighs only, what, 1kg? “If you think that carmakers are spending millions to reduce the weight of a car by grams, that’s a pretty big difference,” says Charlie.

The boys prepare to set off for more posing in the paddocks. Charlie accessorises his blue overalls with a Where’s Wally? red bobble hat, his long fair hair streeling out underneath. Will shrugs on what’s clearly his favourite thing in the Connolly range, a stone-coloured trench coat in unlined vulcanised cotton with a strip of pale Connolly leather under the collar and Connolly-Goodwood branding on the black horn buttons. “It’s quite an intense look,” he says, knotting the belt like Mr Humphrey Bogart in The Big Sleep and looking uncharacteristically moody.

Then they leave the Governors’ Enclosure in their fancy threads, Charlie contemplating speed, fate and fortune in his big race at 6.35pm, Will wondering if it’s worth betting on Tiger Roll (again) in the Grand National this afternoon.