Different concepts of luxury may be inferred from a comparison of the wedding feast of Charles Bovary and Emma Rouault with the habits of their contemporary the Duke of Wellington. At the Bovary wedding were served four sirloins, six chicken fricassées, stewed veal, three legs of mutton, four chitterlings (with sorrel), brandy, wine, foaming sweet cider, yellow custards, tarts and sweets with an architectural cake comprising angelica, oranges, nuts, jam and chocolate.

The austere Duke’s ‘conception of duty’, David Piper wrote, ‘did not provoke popularity at all times’. His daily routine was tea with bread and butter in the morning, no lunch and an unvaryingly simple dinner of a joint with a pudding and iced water. The difference between the Bovarys and the Duke was a matter not only of taste, but also of aspiration and prestige, although these things are, of course, all muddled. A V&A exhibition called What is Luxury? and English Heritage’s re-presentation of Apsley House, Wellington’s London home, bring these notions under modern scrutiny.

To Gibbon and Ruskin ‘luxury’ meant excess, arrogance, opulence and depravity, but recently the word has enjoyed a semantic evolution. Experts may debate the timeline, but perhaps the first evidence of a change occurred circa 1959 when Ford called a certain model of the Anglia ‘de luxe’ on account of its having a heater and a little extra chrome. Just as ‘design’ was once used to indicate products with exceptional function, beauty and innovation, today ‘luxury’ has usurped the word’s role as an indicator of exceptionality. No one uses ‘designer’ as an adjective any more, other than ironically.

Thus, as the national museum of design, the V&A’s interest in defining luxury. What is Luxury? can be found in the museum’s main entrance, just to the left of the conga lines for the exhibition of luxury brand Alexander McQueen. The setting is dramatic: a dark room with vitrines inset into the blackness. Each is devoted to an aspect of luxury identified by the curators: ‘Creativity’, ‘Innovation’, ‘Expertise’ and on to ‘Passion’, ‘Precision’ and ‘Pleasure’, categories so vast that any real meaning seems to escape. Visitors will see a gold ‘luxury’ skimming stone by Dominic Wilcox, a Raj-era howdah, a 17th-century Venetian chasuble and a modern tea set for connoisseurs of pu-erh. There is also furniture made of human hair, a DNA vending machine and a dial-less watch to assist getting lost: in our over-busy and over-observed age, losing track of time and your bearings are as precious as myrrh or mink.

The effect is rather like a high-concept shop in Spitalfields, but since museums and department stores are historic coevals this may be no bad thing. The exhibition does not, however, much trouble itself with the idea of ‘luxury goods’ as a global business in crisis. French and Italian conglomerates dominate the manufacture and distribution of expensive branded merchandise. One of them, Kering, owns Alexander McQueen. Their focus is China, but China is fickle.

There are reports of fashionable merchandise — black Audis, sorghum liquor, Jimmy Choo pumps and even pedigree Tibetan mastiffs — becoming detritus hither and yon in Cathay while consumers impatiently await the arrival of the next new thing. Big city Chinese are fatigued by familiar handbags. In search of markets, Louis Vuitton now has to open stores in parts of China you have not heard of.

Against this, the V&A exhibition seems a little flat-footed so it is refreshing to visit a refreshed Apsley House, the nation’s gift to the victor of Waterloo, to check on earlier ideas of gratification through acquisition. Apsley House stands at Hyde Park Corner, traditionally marking the most important entry to London. As if to emphasise this topographical status, Lionel de Rothschild installed himself and his new money nearby in West Hamilton Place.

It’s essentially an Adam design of 1777 with an imposing Bath stone portico, a little too imposing, some say, for the rooms behind it. In 1831 a reform-maddened mob attempted to break in and the Iron Duke installed iron shutters. Behind the re-presented shutters you find an astonishing Canova of a naked Napoleon, undressed as Mars the Peacemaker. Before Freud’s insights, it may not have seemed so very odd to have a giant naked effigy of your worst enemy in your stairwell.

On the walls there are spectacular paintings: the Titian ‘Danae’ back from the Prado, the Velázquez ‘Waterseller’, for example. The original mahogany table in the ceremonial Waterloo Gallery is now gone, but it has been replaced by a facsimile with the length and proportions of a military landing strip. There are giant candelabra in Siberian porphyry, an astonishing silver-gilt centrepiece and a dinner service, gifts from Portugal in 1816 as thanks for deliverance from a fully dressed Napoleon.

It is only a short stroll from Number One London back to the V&A, a route that takes you through Knightsbridge and its consumerist Sodom of modern luxury retailing. Here there are jewellers selling watches for six figures. Walk in wearing a mere Rolex and you feel as if you have brought an unwashed ’95 Golf to the Concorso d’Eleganza Villa d’Este. Gulf boys in customised Bentleys squire Gulf girls jetted in for a weekend of champagne and spas and Harvey Nichols. You do not hear much English spoken, Heathrow now being the ceremonial entry point for London.

I am not sure the Duke of Wellington had a conception of luxury. Nor am I sure that the V&A has answered its own question. But Coco Chanel did. She said it’s not the opposite of poverty, but the opposite of vulgarity. If only… As César Ritz knew, ‘Luxury stains everything it touches.’