The British Rail Class 504 was a unique type of electric multiple unit that ran on 1200 V DC third rail with side-contact current collection. All other mainline UK third rail has the electric "shoe" on top of the rail. The type was used only on the Bury Line between Manchester and Bury. They were built in 1959 at Wolverton Works, and the body was a standard type used for several electrification schemes of the time, but the high DC voltage through a side-contact third rail was unique in Britain.

The trains replaced the previous 5-car units built by the Lancashire & Yorkshire Railway for the route, which had inaugurated this electrification scheme in 1916.  All were withdrawn in 1991 when the line was closed for conversion to form part of the Manchester Metrolink light rail system. One unit, is preserved at the East Lancashire Railway.