List of British Rail modern traction locomotive classes
This article lists every locomotive allocated a TOPS classification and all modern traction (e.g. diesel, electric, gas turbine, petrol) stock used on the mainline network since 1948 (i.e. British Railways and post-privatisation). Diesel locomotives. The 1955 diesel locomotive classes are given in brackets where applicable. A large number of different shunter types were purchased by British Rail and its predecessors, many of which were withdrawn prior to the introduction of TOPS. The tables below attempt to list the different types and the different classifications used to describe them as clearly as  possible: Small shunters: under 300 hp. Shunter classes are listed by 1955 class, which puts TOPS classes in ascending order, and generally puts 1948 and 1962 classes in ascending order. Unclassed shunters are placed at the start of the table; TOPS class 07 has been placed so its 1962 class is in the logical place. Type 2 locomotives: 1001 – 1499hp. Locomotive class are listed by TOPS class. Locomotives for TOPS classes 24 and 26 have their original sub-classes shown, as each wholly comprised locomotives from a distinct 1962 class. Class 21 (II) has sub-classes shown as these are  superficially similar but mechanically different types grouped into a single class. Miscellaneous locomotives. Class 99. When British Rail implemented the TOPS system for managing their operating stock, ships capable of carrying rail vehicles were incorporated into the system as Class 99. In order to circumvent restrictions of the application software, these ships were entered on TOPS as locomotives, 'hauling' the trains which they carried on board. British Rail Class 99 has now been allocated to a class of bi-mode locomtives. Builders' demonstrators. These were locomotives built and owned by private firms, but used by British Railways to test them . Unbuilt locomotives. A number of TOPS class numbers were allocated to proposed locomotives, both diesel and electric, which for many reasons were not proceeded with.