they were fitted with the sulzer 12lda28c twelve-cylinder diesel engine producing (later derated to 2580 bhp to improve reliability), and have been used on both passenger and freight trains on britain's railways for over 40 years. despite the introduction of more modern types of traction, as of 2008 a significant number are still in use, both on the mainline and on heritage railways. as of december 2008, 103 locomotives still exist, with 29 working on the mainline.