In June 1905, Cadbury launched its first Dairy Milk bar, with a higher proportion of milk than previous chocolate bars, and it became the company’s best selling product by 1913. George Cadbury Junior, responsible for the development of the bar, has said “All sorts of names were suggested: Highland Milk, Jersey and Dairy Maid. But when a customer’s daughter suggested Dairy Milk, the name stuck.”.   Fruit and Nut was introduced as part of the Dairy Milk line in 1928, soon followed by Whole Nut in 1933. By this point, Cadbury’s was the brand leader in the United Kingdom.  In 1928, Cadbury’s introduced the “glass and a half” slogan to accompany the Dairy Milk bar, to advertise the bar’s higher milk content.

Info gleaned from Wikipedia