 By the time London Underground operations were transferred to the newly created Transport for London ( TfL ) in 2000 , the A Stock trains were already 40 years old . The C Stock trains used on the Circle line , Hammersmith & City line and sections of the District line and the D Stock used on the remainder of the District line were also ageing , and no plans were in place for their replacement . Following lengthy and expensive negotiations , an order was placed in 2003 with Bombardier Transportation for a fleet of new trains to take over all operations on the Metropolitan , Hammersmith & City and District lines . 
