Don't use the word "napkin" to a person of British persuasion, unless you mean to refer to baby diapers or feminine hygiene. Their word for a meal towel is "serviette," though most of them know that you, as an American, are not civilized enough to use the proper word and will know what you mean. If you ask for a "napkin," they will get you the appropriate item even though they may be grinning on the inside.