“I need all your money I can get, so make me a sensible offer.” We Brits may hate haggling but, come autojumbles, it’s gloves off as sellers and punters face each other across a stack of obscure car parts, most of it unpriced – and much of it worth only what someone else is prepared to pay for it.

The subject of the ‘sensible offer’ is a truck horn, and the chap flogging it, Simon Davey, is a dealer in cars and car bits.

His customer wants proof the horn works, so Davey connects it to his van’s battery and gives it a blast sufficient to make us cover our ears.

“I’ll give you 20 quid,” says the customer. “Thirty,” replies Davey. “Twenty-five and you’ve got a deal,” his adversary shoots back. They shake on it.

Welcome to the Haynes Museum autojumble, taking place in the car park at motoring’s Somerset mecca. It’s 9:30 a.m. on a Saturday in June, blowing a gale and raining, of course, but already 100 stands are open for business and visitor numbers are building.

By the end of the morning, 650 will have come. It’s the Haynes venue’s second autojumble – the first was held last year. Exhibitors have paid £30 for a pitch, and entry is £5 per person.

It’s just one of many autojumbles taking place throughout the country this year, the biggest and best known being the International Autojumble at Beaulieu; its sister sale, the Spring Autojumble, has only just happened.

Retired mechanic Ben Haywood, one of the traders at the Haynes sale today, was there last month: “I always do well at Beaulieu, so thought I’d give Haynes a go.”

Also giving Haynes a go is Graham Bunter. The car hobbyist and club racer is putting his faith in Ford parts, and among his treasures are two Pinto cylinder heads at £40 each and five inlet manifolds at £20 apiece.

“The manifolds are undamaged, which is rare, so they’ll sell,” he says confidently.

On another stand, Norman Dunford has two Pinto exhausts and a Crossflow one, each from Mk2 Escorts 1600s, plus a carburettor and intake manifold from an Escort RS2000.

Another pitch is displaying remanufactured sills and gaskets, seals, wiper blades, spark plugs, lights and instruments, either from or for Capris and Escorts.

Steve Crew, here with his nephew, is drawing a modest crowd with his eye-catching arrangement of red Mondeo Mk2 tail-lights.

Also on his tarpaulin are parts from Fiestas and Focuses, a Honda Civic Mk8, a Jaguar XJ8, and a 2006 Audi A4. I reckon he will struggle with his collection of Mondeo wheel-arch liners. He agrees: “After today, they’ll be going in the bin.”

Weekdays, Crew is a car breaker, selling the bits he salvages on eBay and Facebook as well as at events such as Haynes’ autojumble. “If you buy the right car, slowly strip it and sell the parts, you can make five times its price,” he says. “It’s taken over my life.”

Aside from later cars, there’s still business to be done in older stuff. Stuart Sinclair has high hopes for a pair of wings from an MG TF and a side-valve engine from an Austin Cambridge. John Mason-Wenn, 90 years old no less, has been driven from Ross-on-Wye, 100 miles away, by a friend and arrived laden with assorted treasures including magnetos, carburettors and vintage headlights. Nearby, another stand boasts chrome door handles for Ford Populars, still in their boxes.

There are lots of parts like these, many dating from the glory days of the British car industry. Tim White is a bit of a throwback to those times.

He’s selling the replacement panels, chassis, suspension legs, floor pans and subframes that he produces at his business in Frome, using the equipment he saved when his old employer ceased trading.

A few stands along, fellow trader Andrew Welsh says he’s having a good day. He specialises in 1970s to 1990s car parts for which, he claims, demand is growing.

For the Haynes sale he has brought along a mountain of stuff, most notably two unused Morris Marina rear bumpers, the front wing from a Maestro van and headlights from a Mk1 Ford Escort. By close of play, he reckons he’ll have made around £150.

Meanwhile, visitors browse and haggle. The smiles on some speak of dreams realised.

Peter Simmons has an MGB roadster at home but today has bought a few light lenses from a Mini pick-up for his baler (he’s a part-time farmer), some tools and, bizarrely, a horse-shoeing stand – “you rest the horse’s hoof on it,” he explains.

It’s not what I expected at an autojumble, but if you go with an open mind you’ll be surprised what you come away with. Me? I fell for an old Tri-ang circus lorry for £30.