[jinx]

Right, from buster's link

United Kingdom

In the United Kingdom, the name gyros is not widely known; the Turkish "döner kebab" is more common, and the general term "kebab" is more common still. However, soldiers ("squaddies") who have served on the British bases in Cyprus often refer wistfully to the delights of gyros. Doner are a very popular post-pub/nightclub food with many high streets in the UK having a kebab house. The meat on the rotisserie is usually a poor quality ground-meat concoction, rather than the slices of actual meat used in Greece.
These kebab shops were initially primarily owned by Turkish Cypriots, hence the use of the dry, hard "pocket" Cypriot pita in place of the typically doughy, more naan-like Greek pita. The small pocket pitas are difficult to fill without breaking, and so the dish is usually served as a loose assortment in a polystyrene container. Tzatziki is rare, and replaced by generic garlic and/or chili sauce.

[edit] United States

Gyros were introduced to the Chicago area in 1968,[6][7][8] and have since spread to all parts of the country. In the United States, gyros are usually made from sliced lamb, minced beef or possibly a combination of the two. Chicken is a common alternative in many restaurants serving gyros. The pita resembles a Greek 'plain' pita. The most common fillings are generally tomato and onion. The sauce is usually tzatziki, sometimes called "Cucumber", "Yogurt", or "White" sauce. These sandwiches are often served in luncheonettes or diners.
In the United States, many restaurants (and even Greek-American festivals) sell gyros with meat which is pre-formed into strips (as though they had been sliced from the rotisserie) and frozen to meet USDA health standards. Gyro meat is essentially seasoned lamb or beef and sometimes mixed with pork. Some gyro meat is cooked on a rotating vertical spit in the same fashion as Doner Kebab. Some establishments, serving varied menus, choose to grill or pan fry individual strips of the gyro meat to prevent waste.