Cucumber sandwiches on the BBC set of Smiley's People

The chance to watch a BBC unit at work on location is a unique experience. It's strictly a no-fuss, no-frills production with extraordinary professionalism and a lot of hard work.

After hours, there are a lot of good times, many that have to do with eating.

''You can pretty well divide this unit up between those who care a lot about food and those who don't,'' said Jeremy Silberston.

As far as I could tell, nearly everyone on the set of ''Smiley's People'' the British Broadcasting Corporation production of John Le Carre's thriller, a sequel to ''Tinker, Tailor, Soldier, Spy,'' cared a lot about food. Silberston is one of the production managers.

At the center of the unit was Sir Alec Guinness, who plays the rueful spy, George Smiley. He is, of course, the star.

Sir Alec set the style on the set and on the sidelines, and that style was an exquisite courtesy. He entertained cast and crew by telling jokes. He was a genial host.

Sir Alec, as it turned out, also likes to eat. He described with pleasure some of his favorite foods: the Japanese strawberries that grow along the walls in the English countryside; the quail eggs en croute at London's Connaught Hotel; a visit to New York's lovely French-Japanese restaurant, Gibbon; and how he finds lobster a disappointment.

During a break one day, Sir Alec glanced at some cucumber sandwiches set out for a snack, said they were all wrong - much too thick - and then gave a humorous description of how to make them properly.

When I joined up with ''Smiley's People'' in Switzerland, the unit had been on the road for nearly five months; first in France, where everyone ate too much , they said, then in Germany.

In Germany, meals were served on green tablecloths out of burnished-copper pots with, as often as not, music to eat by, according to director Simon Langton , of ''Rebecca,'' ''Therese Raquin,'' and ''I Remember Nelson'' on PBS.

In England, location lunches tended to pork and beans, fried fish and chips, fruit salad and cream.

In Switzerland, the crew enjoyed local specialties as in Berne when lunch took place in a vaulted medieval rathskeller and included platters of boiled beef, leeks, thick-cut carrots, roasted potatoes, platters of cheese, and the wonderful, grainy Swiss brown bread.

Sir Alec - who always took his lunches with the unit, always served himself, refusing offers of help - eyed the dessert, having already consumed a hearty meal.

One evening at the grill of the Bellevue Palace Hotel, where the unit stayed and where Smiley, in pursuit of his arch enemy, the Russian agent Karla, stays, ample attention was given to the menu at hand.

Eventually Langton ordered sausage and beans; Ken Macmillan had risotto; the distinguished English actor Bernard Hepton, who plays Toby Esterhase, had a sort of Swiss cassoulet he'd admired the night before.

Joe Praml, an American actor who plays Skordeno, one of Smiley's bodyguards, contemplated the chocolate mousse - and then had two.

There is something very appealing about watching filmmakers perform their magic on location, pulling doves from their sleeves and snow from pails of salt.

As the unit made its way from Berne to Brienz, the conversation on the bus was about chocolates and scenery. You had the sense of a peripatetic, old-fashioned theatrical troupe, with all its inherent romance and a lot of jokes.

Brienz is famous for its woodcarving industry, where you can get rolling pins with edelweiss cut out for decorative cookies.

Sir Alec, Langton, Hepton, and the French actor Michael Lonsdale, who plays the Russian Grigoriev, went into Brienz village for a seafood dinner with fish soup, fish pate, smoked fish, and boiled fish.

In England, ''Smiley's People'' moved to Nottingham, where the endlessly inventive design team turned an old railway bridge in that northern city into a bridge in Berlin, having been denied permission by the East Germans to film in Berlin.

At lunch with Sir Alec in an Italian bistro in Nottingham, there was seafood salad and veal, but Sir Alec ate lasagna and worried that everyone might not get just what he liked to eat best.

He chatted about T.S. Eliot, whom he had known when he appeared in ''The Cocktail Party,'' and he told of the time Gordon Jackson played butler at a dinner party. Sir Alec, it seems, had American friends who raved about ''Upstairs, Downstairs,'' especially Mr. Hudson, played by Gordon Jackson.

When the American lady in question heard a voice say, ''Can I get you something, Madame?'' she turned to see Mr. Hudson - in person.