London — Britain, beware. A tidal wave of American popcorn is ready to roll across the Atlantic toward you, and you may never be the same. The British know about popcorn already, but they eat it in cinemas, not at home, and they do terrible things to it, including drenching it in sticky caramel liquid.
Now the Popcorn Institute in Chicago has enlisted the United States Department of Agriculture in a campaign to win new markets abroad. In Britain, this means changing popcorn's image.
''We want the British to get away from all this caramel and sugar,'' says an enthusiastic official in the US Embassy in London.
''Popcorn is a savory snack, and it's a health food as well.
''Eat it with salt and butter, as Americans do - that's what we're telling people.
''Eat it with cheese. Eat it with garlic pizza flavorings. Put tandoori (curry) seasonings with it. Use peanut butter.
''We've served it to Britishers here at the embassy with rose water and cinnamon. My own favorite is popcorn with lemon and dill. . . .''
Popcorn has just gone onto school menus in Hertfordshire, tossed in melted margarine (and with a dash of sugar). Major supermarket chains are beginning to stock it.
British families are asking the embassy for recipes. One of the two breakfast-TV shows about to start here is planning a popcorn feature. Britain's large Indian and Pakistani populations, which eat wheat as a staple, are also taking to it.
And still the popcorn potential is mouth-watering. Americans eat 41 quarts of it a year while the British manage only one quart each. The climate is not warm enough to grow hard-kernel corn, so it must be imported from the US and elsewhere.
Yet resistance is also high.
Popcorn is perceived here as junk food pure and simple - and utterly, hopelessly American as well.
The British don't even call corn cornm. They call it maizem.
When bowls of popcorn came out at a promotion party for food and children's magazine editors recently, the guests were incredulous.
''But when they tried it with rose water and cinnamon and all the rest, they liked it,'' says the embassy man. ''We had to refill those bowls three or four times. . . .
''All over Europe, people have this sweet tooth. It's something to do with the war, I think - they couldn't get sugar then so they pour it on now. . . . We have to change this as far as popcorn is concerned.''
One of the promoters' highest hopes here is to bring popcorn - without caramel - into British homes, so that families will crunch it in front of their television sets.
With Britain about to be hit by a television explosion, from cable to satellite broadcasting to breakfast TV, popcorn's potential seems even larger.
Whether enough true-blue Englishmen can bring themselves to eat it, however, even with rose water and cinnamon, remains a question which has only just begun to be popped.