 The government backing came as part of a proposal to nationalise the railways, which would require a standard fleet of locomotives to promote economies in production and maintenance.The nationalisation proposal was abandoned; instead, the government passed the 1921 Railways Act, which grouped the railways into the "Big Four" in 1923.Building of the second batch went ahead to retain skilled labour at Woolwich, but the fabrication of 119 boilers for allocation to the kits of parts was contracted-out because of limited production capacity at Woolwich and Ashford; the North British Locomotive Company built 85, Robert Stephenson and Company 20, and Kitson & Co. 14.