During the First World War there were severe shortages of men, horses and vehicles which hampered the dairy business, reliant on the timely distribution of its products. United Dairies was formed in 1917 when Wiltshire United Dairies, Metropolitan and Great Western Dairies, and the Dairy Supply Company merged in an attempt to pool their resources and keep their companies operating until the end of the War. However, the merged company was so successful under the chairmanship of Reginald Butler that it began to expand, acquiring other dairies and creameries across the UK.
In the late 1920s, United Dairies helped pioneer the sale of pasteurized milk in Britain.
The company was a large user of milk trains. Milk tank wagons were a common sight on the railways in the UK from the early 1930s to the late 1960s. While rival company Express Dairies preferred the Great Western Railway, United Dairies used the Southern Railway. Introduced to transport raw milk from creameries to food processing units in remote locations, milk trains were the last railway-based system before the mass introduction of pasteurization and the resultant industry use of road transport.
By the early 1950s, United Dairies had become the largest dairy products company in the UK. However, the company had become inefficient and in an effort to improve its operations United Dairies merged with its long-time rival Cow & Gate in 1959 to form Unigate. The dairying side of Unigate’s business was sold to Dairy Crest in 2000.