From 1914 until 1969, when it was absorbed into WMPTE, Birmingham City Transport had various periods when they hired buses for evaluation. These demonstrators were tried out for a variety of reasons such as tramway feeder route development, expansion of the bus fleet to meet increasing passenger numbers, abandonment of tramcar services and expansion into the newly built municipal housing estates in the interwar and post-war periods. It tried out a wide variety of vehicles provided by both chassis and body manufacturers. This was to compare different manufacturers products, with a view to purchasing a substantial number of buses. BCT was the largest municipal operator in the UK, so this was a potentially lucrative opportunity for manufacturers. There were years when Birmingham had a large number of buses on hire in order to assess their performance, fuel economy and durability. 1923/4, 1929–1934, 1937, 1946/7,1955–1958 and 1960–1967 were the peak years for vehicle trials, of which very few were successful due to BCT's exacting requirements as well as their wish, where possible, to support local industry. A fascinating selection of buses were tested over the years.