VISITORS TO LONDON may not be able to wangle an invitation to Buckingham Palace for lunch, but you can certainly shop were the queen shops and put the same delectables on your table.

Certain British trade companies are permitted "to style themselves By Appointment to Her Majesty the Queen." The chosen few are entitled to display the royal arms but not to fly the royal standard. These royal warrant holders are the people who supply the goodies for the regal kitchens.

For those of us with discriminating taste, there's nothing more reassuring than spotting the royal arms above a shop door. To put together a royal luncheon, start at Fortnum and Mason on Picadilly. They are grocers and provision merchants to Her Majesty. Here you can pick up biscuits, tinned oysters, potted meats, bottled chutneys, wine and perhaps a bit of Stilton.

A word of warning: On your first foray into F&M, don't mistake the sales clerks in their black tailcoats for members of the House of Lords and call them "Your Grace"--you'll have blown your cover.

For your entree, how about a woodcock or two? A trip to John Lidstone, the butcher, takes you to Lower Belgrave Street. Lidstone's is, in fact, purveyor of meat to the Queen Mother. The shop is a miniature store on a residential street, with the prestigious coat of arms above the door.

On a recent visit, I saw a single pheasant hung in one window above a chain of discreetly displayed sausages. In the other window, a few bright-red chops sat in majestic isolation. Inside the shop, two ruddy butchers in pristine white plied their trade on huge maple blocks and then handed neatly wrapped parcels to a uniformed chauffeur. Outside the shop, a matron in a large hat sat in a limousine shouting through the open shop door in a shrill voice, "Mind you trim all the fat."

There are no prices displayed and one ought not ask.

If Lidstone's hasn't enough selection for you, Harrods is the place. Before entering this paragon of department stores, look above the display windows and you'll see dozens of brightly colored coats of arms. Through its long history, Harrods has been a warrant holder to many a crowned head.

The food halls are second to none. The walls are covered with superb Moorish-style tiles depicting various edibles. In the meat hall there's a lovely bronze peacock, tail unfurled, above the clock. Hanging above the white-hatted clerks you'll see a representative of every type of sausage and salami known to man.

Because you're in Britain, why not go ethnic? With visions of Balmoral brunches dancing in your head, try some haggis. You'll see the Scottish version of foie gras at the sausage and ham counter. Sliced haggis makes a first-class pa te'.

For dessert, your best bet is chocolate. This requires a visit to Charbonnel et Walker at 28 Old Bond St., just north of the Burlington Arcade. The royal confections are placed in chic dark-brown boxes bearing a coat of arms embossed in white. House specialties are individually initialed chocolates and the chalky-tasting violet and rose creams the English upper class likes so much. The chocolates cost about $20 a pound. If you need an immediate fix, the individually wrapped bouche'es are 35 pence each.

The alternative for dessert is a cake or some ice cream from Lyons--yes, the same Lyons as the corner tea-shop people who produce overly sweet, pastel confections that are washed down with the kind of tea that was probably brewed in Crimean army camps.

Lyons holds several royal warrants and is, in fact, the caterer for the royal garden parties at Buckingham Palace. Needless to say, one doesn't go to one of those fetes for the food.

For the perfect ending to your lunch try H.R. Higgins, coffee merchant by Appointment to Her Majesty the Queen, at 42 South Molton St., off Oxford Street. The shop is a quaint, polished wood-and-brass affair, with beautiful antique coffee cannisters.

Higgins carries 26 different coffees, all with romantic names that conjure up visions of sailing ships and the Empire: mysore, hanover, creole, java, sultan (a strong coffee combining the bland flavor of South American with the bite of West African).

I asked for the very best Mr. Higgins had to offer, and was presented with a bag of kibo chagga beans. Kibo is the summit of Mount Kilimanjaro and the coffee is produced by the Wa-Chagga tribe that lives on the mountain slopes. It's picked by hand and washed in streams from the Kibo Glacier. This coffee is then dried in the "pure mountain air."

I was vulgar enough to ask Higgins what the favorite brew at the palace was. Appropriately, the question went unanswered.