<P> Although chocolate bars had their beginnings in the mid 19th century, their sales grew most rapidly in the early - 20th century . Milk chocolate was invented in Switzerland by Daniel Peter and Henri Nestlé in 1875 . In 1897, following the lead of Swiss companies, Cadbury introduced its own line of milk chocolate bars, with Cadbury Dairy Milk, produced in 1905, becoming the company's best selling bar . In North America, Ganong Bros., Ltd. of St. Stephen, New Brunswick, Canada developed and began selling their version of the modern chocolate bar in 1910 . The Hershey Chocolate Company took the lead in the U.S. </P> <P> The world's largest "chocolate bar" was produced as a stunt by Thorntons plc (UK) on 7 October 2011 . It weighed 5,792.50 kg (12,770.3 lb) and measured 4m by 4m by 0.35 m . Some of the oldest preserved chocolate bars are two pieces of white and dark chocolate made between 1764 and 1795 for the king of Poland, Stanislaus Augustus Poniatowski, as a gift for his courtiers . Each bar, possibly made by the royal confectioner in Warsaw, bears the King's monogram, SAR, and is on display in his summer residence, Palace on the Water, in Warsaw . </P>

What is the oldest chocolate bar still in production in uk