Phase 2, the introduction of three prototype trains (APT-P) into revenue service on the Glasgow – London Euston route, did occur. Originally, there were to have been eight APT-P sets running, with minimal differences between them and the main fleet. However, financial constraints lead to only three being authorised, after two years of discussion by the British Railways Board. The cost was split equally between the Board and the Ministry of Transport. After these delays, considerable pressure grew to put the APT-P into revenue-service before they were fully ready. This inevitably lead to high-profile failures as a result of technical problems.