The original four-finger version of the bar was developed after a worker at the Rowntree's factory, York put a suggestion in the recommendation box for a snack that a "man could have in his lunch box for work".  The product was launched in September 1935 in the UK as Rowntree's Chocolate Crisp, and the later two-finger version was launched on May 15, 1936.  Rowntree's Chocolate Crisp was renamed Kit Kat Chocolate Crisp in 1937, and after World War II just Kit Kat....

The original four-finger version of the bar was developed after a worker at the Rowntree's factory, York put a suggestion in the recommendation box for a snack that a "man could have in his lunch box for work".  The product was launched in September 1935 in the UK as Rowntree's Chocolate Crisp, and the later two-finger version was launched on May 15, 1936.  Rowntree's Chocolate Crisp was renamed Kit Kat Chocolate Crisp in 1937, and after World War II just Kit Kat.  The following advertizements ran from 1974-1984. Cricket Umpire:  Kit Kat, give yourself a break (1974) Col Ticket Office:  Kit Kat, give yourself a break (1974) Col Beach Ball:  Have a lovely holiday break (1975) Col Rowing Boat:  Have a lovely holiday break (1975) Col Shoe Shop:  Kit Kat, give yourself a break (1975) Col Camping Holiday:  Have a lovely holiday break (1975) Col Ploughing:  Give yourself a break (1975) Col Shy Break:  Give yourself a break (1976) Col Hanging Around:  I expect he's hanging around outside (1982) Col 1980:  Have a break at the 1980 price (1983) Col Free Bar Offer:  It's too good to last (1982) Col Interlude:  Give yourself a break (1976) Col Andy:  Have a break, have a Kit Kat (1976) Col Punch:  Have a break, have a Kit Kat (1977) Col Guessing Game:  Good Heavens, I certainly wasn't doing that Madam (1977) Col Human Pyramid:  Have a break, have a Kit Kat (1978) Col Nice Place:  Have a break, have a Kit Kat (1979) Col Guards Van:  Have a break, have a Kit Kat (1980) Col Word Break:  Still only 14p Kit Kat (1982) Col That Big:  Have a break, have a bigger Kit Kat (1983) Col – Featuring Sue Pollard and Roy Kinnear 1980 (Rev):  Have a break at the 1980 price (1983) Col Spot the Ball:  Don't miss it.  Kit Kat, Blue Riband, Breakaway (1983) Col Middle of the Road:  Middle of the road! (1984) Col Scared Crows:  Have a break, have a Kit Kat (1984) Col Pop Group:  You can't sing, you can't play, you look awful.  You'll go a long way (1984) Col