It might be obvious, but buying a "fabulously British" Jack Wills polo shirt in Southwold immediately marks you out as different from the bling-obsessed young mum who frequents a retail park to buy a bright pink Paul's Boutique purse. Or so you might think. Actually, argues journalist and consumer broadcaster Wallop, these are both decisions based on similar ideas of class aspiration, and Consumed is his entertaining attempt to understand how we define ourselves through our consumer choices.

He does so by making the definitions for us. He names the mega-rich "Portland Privateers", after the private London clinic in which they give birth to Hermiones and Oscars. There's the "Wood Burning Stovers", who pad about in Birkenstock sandals and eat from organic veg boxes, "Asda Mums" and, at the bottom, those Paul's Boutique fans, the "Hyphen-Leighs", who have a penchant for naming their children Kaydie-Leigh. As something of a toff himself, it's impossible not to read a little derision into his descriptions of the Hyphen-Leighs. But happily, as Wallop whizzes through the determining factors of social status in food, family, property, clothes, education, holidays, leisure and work, he pokes as much fun at the ridiculousness of the class insecurity that drives sales of £3,500 Mulberry ostrich handbags.

But for all the interesting social history, and his achingly true observations  taking in the clever packaging of the Waitrose Essentials range, Farrow & Ball paint and Jo Malone "scent"  the general tone of Consumed is detached amusement at how suckered we are by brands. And in the end, it means Wallop doesn't achieve much more than reinforce the stereotypes he has so much fun building.

Harry Wallop's qualifications to investigate the subject of Consumed are twofold. As a former consumer affairs editor of the Daily Telegraph, he will have paid as much attention as any man living to the share price of Marks & Spencer and the social semiotics of its ready meals. But, as his book sets out with rather winning ingenuousness, he's a solid-gold old-school toff to boot.

Accordingly, Consumed is primarily a breezy journalistic zip over the way class operates now  bolstered by interviews with case studies, statistics from the ONS and a historical background sketched in from newspaper archives and the works of Dominic Sandbrook and David Kynaston. It's also, sneakingly, a more personal story  informed by Wallop's aristocratic parents and working-class in-laws.

His unexceptionable thesis is this: the classless society dreamed of by such prophets as John Major and Karl Marx has not come to pass. Nor will it. But a change has taken place: in our consumer society, class no longer depends so much on how you earn your money as on how you spend it (which, Wallop says, "seems to me to be progress of some sort").

Wallop gallops over the way this plays out in chapters dealing with food, family, property, home, clothes, education, holidays, leisure and work. The focus on consumption qua shopping promised in his subtitle is pretty loose, but that's proper. The way class is entrenched in education and property ownership is after all still a huge part of the story.

We're all familiar with the ABC1/C2DE segmentation of class made by the National Readership Survey, but things have come on since then. Big marketing companies such as Acorn and Mosaic scrape vast amounts of data from hundreds of sources to segment Britain, postcode by postcode, into dozens of groupings with labels such as Burdened Optimists, Sprawling Subtopias and Multi-Ethnic Crowded Flats. Wallop puts all these aside (though I wish he'd found space to set them out in full in an appendix) and makes up his own class groupings.

At the top are the Portland Privateers  AKA the international super-rich, so named for the private clinic where they like to give birth. Then there are the Tatler-reading public-school hearties to be seen on the Look At My Fucking Red Trousers Tumblr, named Rockabillies for the Cornish resort on which they descent like drunken locusts each summer. In the middle are the Middleton Classes  AKA lower-middle-made-good. At the other end of the scale are the Sun Skittlers (red-top readers and unironic players of skittles, content to remain so), the Asda Mums, who eat tinned food so their kids can have branded treats, and the bling-festooned Hyphen Leighs. These are so called because of the proliferation of new kids' names such as Demi-Leigh, Chelsea-Leigh, Tia-Leigh, Kaydie-Leigh and Lilleigh ("which sounds like a sanitary product", Wallop sniggers)  all of which apparently derive from Kayleigh. These are Marillion's children.

And, yes, you: hypocrite lecteur. My wealthy, liberal, butcher-block-owning, tamarind-paste-acquiring, fiddly-Italian-coffee-pot-using friend. You're up to your neck in the class system too. Wallop claims that the Guardian  at least going by mentions of such phrases as "middle class"  is the most class-obsessed of all the newspapers. Its readers are, in large numbers, what Wallop calls Wood-Burning Stovers.

As you may guess, there's some rampant social stereotyping going on here, and a gentle salting of actual snobbery. Wallop's not shy to use the terms "low class" and "lower class" (though he forgoes the Auberon Waugh scare quotes: "'working' class"). Sometimes he is writing social analysis; at others, he can't resist a spot of U and non-U. At the Telegraph office, he says, a Boots Shapers meal deal is "for secretaries and junior staff in the advertising department only", and later wonders "who, apart from junior in accounts, takes a banana to work in its own little, aerated plastic case?" He identifies John and Pauline Prescott as "archetypal Blackpool Posh" ("the showiest end of the Middleton classes, who have made the move up to the top, but failed to completely shake off their Sun Skittling background: too much makeup, blousy dresses and blousier hair").

Gags about smelly candles, Asda caviar and Jo Malone perfume (oops, scent) are plentiful. Analytically, there are avenues left underexplored. Wallop touches on the notion that the increase in discretionary spending and leisure time that underpins the consumer society he describes is down to women being freed from housework  but that bears far more discussion. Likewise, his starting point of 1954 makes sense, but there's room for a much longer view on the history of class and conspicuous consumption.

Little milestones in social history  the chicken kiev ready meal; the Habitat garlic press; the first package holidays  are deftly handled. Some fine and interesting details emerge, too. I didn't know that every single member of Tony Blair's first cabinet listed "football" among their interests in Who's Who. I was pleased to have Wallop's assurance (on the authority of "those that know") that Her Majesty the Queen says "loo", and that the Duchess of Bedford shopped at Costco. And if you're anything like me, you'll exclaim on page 40: "So that's what happened to Sunny Delight!" ("after reports suggesting it turned toddlers orange [...] it has all but disappeared from view").

There's some old-school shoe-leather reporting here, also. The book's best statistic is a frequency analysis of Juicy Princess children's buggies. Wallop reports: "Stand outside a branch of JD Sports in Beckton, as I have done, and you will spot one every 45 minutes." Does he mean every 45 seconds? The picture of our man standing there for hours, solemnly marking off five-bar gates in his notebook as the sun tracks across the sky, is one that will haunt me.

Some of the most original and delightful material, anyway, is the stuff  I'd say "unintentionally hilarious", but I think Wallop knows just what he's about  concerning his own background. He identifies himself as having moved class  thanks to having such things as a job, no stately home, and a non-posh wife  into a place somewhere between Rockabilly and Wood-Burning Stover.

Yet he bubbles with anecdotes of the "assorted earls, countesses and Viscounts" from which he received his childhood Christmas presents; mentions his cousin the Earl ("so partial to a Greggs sausage roll that he invested some of the family fortune in the company's shares"); assures us that his father's title, as younger son of an earl is "about the lowliest one there is"; and recalls his fear, at prep school, of the comprehensive kids "and the cans of Vimto they would lob over the fence on to the eighth green of our golf course".

Wallop even boasts that he lost his foreskin to the same mohel as Prince Charles  which I can't help thinking will make an excellent icebreaker if he ever finds himself invited to a reception at St James's Palace.

 Sam Leith's You Talkin' to Me? is published by Profile.