Although the Mars factory was set up and owned by an American, Forrest Mars Sr., the Mars Bar was developed and first produced in Slough over 70 years ago. Interestingly, Britain ranks as Mars' biggest market and not the U.S.

In 1932 Forrest Mars Sr. decided to start up a confectionery business in Britain. With only £5,000 to achieve his goal, he began with second-hand equipment and a small kitchen on the Slough Estate, living in a one-room flat behind the 'factory'. The recipe for the Mars Bar was based on the American Milky Way, adapted to suit the British preference for sweeter confectionery.

Mars Limited was registered on 17 May 1932, and on August Bank Holiday Monday, in his freezing kitchen, and with only four employees, the first Mars Bars were produced.

Forrest Mars realised he would not be able to manufacture his own chocolate for many years, so these early Mars Bars were in fact coated in chocolate bought from Birmingham-based Cadbury.

Mars was unusual for its time in introducing benefits for its workers. These included a pension plan, an in-house doctor, a cafeteria and a newsletter.

More than seven decades later, the Mars Bar is still popular and has been reproduced in different sizes, as ice cream and as milk drinks. Mars merged with Pedigree Masterfoods in 2002 into Masterfoods. The company has 2000 employees and produces 3 million Mars Bars a day.