Whenever Sir Benjamin Slade sniffs out new money, he homes in on it like an Exocet missile and asks how it was made because, he says, he genuinely wants to know.

As someone who, at 16, inherited a title but no money, he has had to make several fortunes to buy back the accoutrements that define his upper-class status. It has been damned hard work and now, irony of ironies, he finds himself, at 61, divorced, happily attached to a long-term partner called Kirsty who comes from a good family herself, and with all the stuff of his class - but no heir.

Can you buy your way in?

“Of course you can,” he bellows. “They always did. All you have to do is make shedloads of money, learn the code, and life's your oyster. The class system is a game that's played behind walls. To keep things going you always have to marry a bit of money. My folks forgot the habit for about eight generations and it was a nightmare. We needed dosh. You've got to be entrepreneurial to survive. The whole thing is a nightmare, quite exhausting.”

He is an amiable man, a welcoming host and a bit of a ham. Most of his anecdotes are about his own misbehaviour, but he strikes me as harmless, and it occurs to me that misbehaving is a mark of the confidence that comes not just from a public-school education but from knowing that you belong in your chosen milieu. He didn't always, and that is doubtless why Sir Benjamin enjoys it so much.

“I wanted my roots back,” he explains, perching on a fender in front of a wood fire in the library of Maunsel House, the 13th-century family seat near Bridgwater in Somerset, that he bought as a listed wreck and has renovated and developed into a conference and wedding business. Three of his dogs vie for attention: Brictwold the Saxon, named after an ancestor; Prince Charles and Gerald Westminster, thus named because when they visit grand houses he likes to put their names in the visitors' book. “It means that I shoot with the right people.”

The room has no books but it does have a stuffed crocodile wearing what looks like a German helmet, and a stuffed bear topped by a Tommy Cooper fez.

“Course I bought the bear in. I ain't going hunting bears. It's expensive, and I'm not a very good shot - he'd get me. He often stands in line and greets the guests, which is terribly funny. He sometimes ends up in bed with the bride and groom, so he's quite busy. Every house has to have a bear. And a couple of suits of armour.”

Sir Benjamin made his money by setting up a shipping container company, and was initially regarded by his relatives as a new man. “A spiv because I'd made money. They don't think sometimes that I'm out of the top drawer at all.” Because you're indiscreet? “Hopeless. Actually my family made their money by killing French people. We were into fighting, drinking and hunting.”

We digress. He is about to tell me how he redeemed himself. “Then I went and bought a grouse moor and I was made. Great landed magnets. People with pedigrees and ambience and castles said, ‘Hello, how's it going, old boy? Nice to know you.' It was bloody marvellous. I said, ‘Having a slight problem, ain't much heather and hardly any grouse'. They thought I was trying to fend them off and got even nicer.”

Just as other classes have codes for recognising each other, so the upper class is a tribe with its own behaviour and attitude traits, he explains, and naturally it doesn't follow any logic because if it did it would be less exclusive. The lavatory is a dungy, a bog, a s***house, a ladies' room - anything but a toilet. At dinner you use a table napkin but never a serviette. And you must be careful how you spend your money. “If you get a pink striped Rolls-Royce everybody knows you can afford a Rolls-Royce but they say it's not been spent the right way.”

Sir Benjamin has several cars, but likes his Ford Ka because it can get him to London for £15. He has never sold a car in going condition, and his favourite is the Volvo that has done 324,000 miles, which he intends to burn on a raft like a Viking funeral. There is also an ancient Saab, which the dogs like. “We drive cars until they drop. I can get away with that. If you're new money you have to buy something like a Ferrari. It's much easier being old money.”

He notes, too, that he is wearing the uniform: a checked jacket, reminiscent of a benign Toad of Toad Hall, that he bought a decade or two ago from a friend for £50. He wears this over mustard cords, brown brogues and a Longines watch. “It's best to inherit a few clothes because you don't want to look as though you arrived yesterday, but I have a tailor called George. He makes suits for the nobility. You also have to be hysterically funny or terribly knowledgeable - that's more important than diamonds. A lot of my friends are self-made and they dine out all the time because they're bloody amusing. Essentially you've got to sing for your supper, make plenty of money and learn the ways to spend it. We are pack animals.”

Lunch is served in the dining room by one of his 19 staff, then he shows me round the house. It is warm, comfortable and a tad distressed in places, a bit like an upper-class theme park with all the ingredients on a plate for the delectation of the middle classes. “If you sell class, they say, where did you get that paint? The middle classes are trying to learn all the time.”

He is looking for a Slade to become his heir. Does the heir's class matter? He says that it would be nice if he were clubbable, interested in books and furniture and trees and gardens. And not very new money.

“A wide range of interests, that's what you want. The trouble is, you get somebody who's run a factory and made £50 million, or a farmer whose sole job was to pull cows' tits - very boring. It would be nice if they'd fought in a battle or could ride a horse well. I was always falling off my horses, but there we are.”

Someone like him, then. A member of the tribe. And someone who can afford the £50,000 or so that's needed for a new drive.

‘What they aspire to are white carpets and fake grass'

It's the hair that you notice first in Sandbanks. All the women look as though they have just had a blow-dry. Their nails are professionally tended, their legs toned, their heels spindly. High- maintenance and, in the local vernacular, classy.

That's the trouble with trying to talk about class on this notoriously expensive stretch of the Dorset coast: the word is surrounded by confusion. I'm talking about class as a noun that means tribe, but people here often use it as an adjective. Not that class isn't an issue - this is the land of new money, a few square miles where one resident reckons there are 100 Bentleys. I have never previously seen so much conspicuous wealth outside a metropolis. Or felt so inadequately groomed.

The big money began to arrive in 2000 when a canny estate agent called Tom Doyle performed a sleight of hand that gave Sandbanks the reputation of being the fourth most expensive location in the world. It probably wasn't, and he admits that it isn't now, but the sale of a £1 million - or £695 a foot - flat enabled Doyle to get it logged on a global league table collated by a New Yorker who, he admits, had no idea that Sandbanks wasn't close to London. He may have forgotten to mention that. But the label stuck and now this sandy spit overlooking Poole harbour is a strange mixture of palm trees, 1930s bungalows, building sites and multimillion-pound palaces with concrete lions outside and footballers, their wives and ludicrously successful business people inside.

There's old money around, too, but it's discreet - some of it up the hill in Canford Cliffs and Branksome Park, a wooded conservation area where houses that look like spaceships are landing in the broad avenues of mock-Tudor piles. The new-money properties are still in the minority but, as their owners parade their trophies and an infrastucture of hairdressers, gyms, eateries and estate agents emerges to cater for them, it's impossible to miss the invading culture.

At Café Shore, Julia Brafman, Bulgari sunglasses on her head, perches on a leopard-print chair. Cleverly, in turning a greasy spoon into a high-end restaurant (caviar with traditional accompaniments, £95; Château Mouton Rothschild, £470) and a vast bar where you can have a burger for a tenner, she has provided a social focal point for Sandbanks's new residents.

“I like my bling,” she says - and her formula for sophistication certainly attracts expensively turned-out clients. There's a Maserati outside, lots of Mercedes in the car park across the road, and the middle-aged men who bring their girlfriends for lunch (most are too attentive to be with their wives) wear beautifully cut jackets. The dress code is smart casual, but Brafman likes to be flexible to accommodate the labels. “If they come in at 6.30pm wearing Ralph Lauren and Gucci sandals ... we do try not to upset people. You do understand what I'm trying to say?” Perfectly.

Brafman is a Bethnal Green girl by birth and keeps the accent. Her parents worked their way up from fruit and veg to running Lucy's, one of London's first designer chains. Her Sandbanks venture has yet to show a profit but that doesn't stop her driving a CLK convertible, or educating her four children privately. “It pays off in respect for elders, being polite, and it affects their social life. My eldest son is friends with Mick Jagger's son and goes to his house, so they see the lifestyle.”

When I ask how she would define the class of local people, she replies “stylish”. And how do stylish Sandbanks people assess each other? “I wouldn't say it's class. They want to know who they want to know. A lot of networking.” In another bar, I meet a young man who is wearing £10,000 of diamonds because it's what his generation does: “You look at TV and stuff and everyone is glamorising themselves to look like they're classy.” His friend mentions his £3,000 Cartier watch, though he says that flash cars aren't classy because finance options mean that anyone can have one these days. As Tom Doyle - the son of a painter and decorator from Ladbroke Grove and now the owner of two Bentleys and a house in Branksome Park - puts it with a smile: “People here judge each other by how much money they've got. Education never comes into it here; accent doesn't matter. It's what sort of car you drive, how big is your boat? What school do your children go to? Class is all about money and how you lead your life with that money.”

Jack Holsgrove has seen Sandbanks change. A self-made property developer who built middle-class estates, he bought his present home in 1972 for £60,000. The view is stunning and the land is now worth £5 million, but Holsgrove rejects the entreaties of developers waving cheques. He's 86, where else would he live, he reasons, but in truth he doesn't want to engage with the culture that revolves around money rather than people. When he employed men he kept them on until retirement, protected them if his schemes lost money. Today everyone works on contract. “It's all about money here. He's got more than me. I want more. The people who buy houses don't occupy them, they treat it as an investment. You don't talk to them. There's no community. People just show their wealth.”

Steph and John Stevenson, both from middle-class backgrounds, run a chain of hairdressers in the area. Their 4x4 Mercedes, Steph's Jimmy Choos and the liveried commissionare outside their Canford Cliffs branch make it clear that they are not averse to playing the Sandbanks game, but as they are not residents they also stand slightly outside it.

“The problem is that people confuse style and class,” says Steph. “They're different. Kids today follow their icons in terms of fashion - it's a lifestyle choice in which everything looks amazing. There's a uniformity about it: the white carpets, white kitchens, fake grass. That's what they aspire to, not to landowners and green wellies.

“You can reinvent yourself now, buy into a class and do what used to take generations, send your son to Eton and into an old boys' network. I think we're going to end up classless like the US.”

Michelle Harrison is a director of the Henley Centre, which observes social trends in Britain. “There has always been new money but at the moment celebrity culture is seen as an alternative route to money and a particular type of aspirational bigticket consumption,” she says.

“They [celebrities] don't normally have the education associated with the middle classes, but they have money and they provide a statement that is a visual representation of success.” She identifies one other new group, also small but socially significant. “There are people earning big money in the City who were not born into the aristocracy but are buying up estates and adopting aristocratic hobbies like shooting. It's what's going on at the top end that is changing our notions of class.”

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