The Nestle factory in York - once the country's leading 'chocolate city - sends five million of the snacks off its production line every day; that's a billion each year, and they're all sold in the UK.
Historic confectionery firm Rowntree's first trademarked the Kit Kat name in 1911, but they did not begin to manufacture chocolate using the brand until 1935. A worker at the York plant suggested creating a cheaper chocolate bar marketed to the working man, but the use of wafer made it popular with the masses, as it was more of a palate cleanser than solid chocolate. Its original name was Chocolate Crisp, and it adopted Kit Kat two years later.
During the war, Rowntree's had to change the Kit Kat recipe due to rationing, and were unable to use the distinctive red and white packaging - instead they produced a blue wrapper.
Its popularity grew in the 1970s, when Rowntree's updated their Victorian factory and introduced new technology which enabled them to boost production. Nestle acquired the company in 1988, and further investment in 2010 allowed them to increase Kit Kat output to the current levels.
York remains the 'Kit Kat HQ' and is also home to other Nestle brands including Aero, Polo, Yorkie and Milkybar.