List of British Rail unbuilt locomotive classes

There have been a number of TOPS class numbers assigned to proposed locomotives in the UK that have not been built for one reason or another.

Diesel locomotives

Class 18 – A proposed new Type 1 locomotive proposed in the mid 1980s. A 1988 proposal was for a 6-wheeled 800 hp locomotive with a maximum speed of 50 mph, similar in concept to Class 14.^[1] No prototype was constructed.

Class 38 – Projected classification for new generation of Type 3 freight locomotives in the 1980s. The Class 38 was dropped in favour of the Class 60.

Class 41 – The third use of Class 41 was for a proposed class of Class 60 locomotives with 2,500 hp engines in the early 1990s.
Class 48 – The second use of Class 48 was a proposal for a new class of locomotive for the 1990s, with gearing differences for slower freight work or higher speed loco-hauled for InterCity or parcels trains. The proposal included using proven technology for engines and electrical systems to avoid lengthy introduction and development costs associated with developing new technology.

Class 51 – Projected classification for the proposed "Super Deltic" locomotive intended as a follow on from the Class 50 and Class 55.^[2]^[3]^[4]^[5]
Class 62 – Projected classification for proposed Type 5 coal train locomotives in the early 1990s.
Class 65 – Projected classification for proposed 4,000 hp freight working locomotive intended for liner trains.

Class 75 – Spare classification for projected "super electro-diesel" follow on from Class 73 and Class 74.

Class 88 – The first use of Class 88 was for a proposed electric version of the Class 58, powered through 25 kV AC from overhead wire.
Class 93 – Proposed electric locomotive for use on the West Coast Main Line as part of the InterCity 250 project.

^ Locomotive Rivals from Across the Pond. D. Clough. Rail (magazine), issue 805, Jul-Aug 2016.
^ Haresnape, Brian (June 1984) [1982]. 3: Production Diesel-Electrics Types 4 and 5. British Rail Fleet Survey (2nd ed.). Shepperton: Ian Allan. p. 6. ISBN 0-7110-1450-7. CX/0684.
^ Allen (1981), p. 19
^ Webb (1982), p. 91
^ Nock 1985, p. 75

Allen, Geoffrey Freeman (1981). The Eastern Since 1948. I. Allan. ISBN 9780711011069.
Nock, O.S. (1985). British Locomotives of the 20th Century: Volume 3 1960-the present day. London: Guild Publishing/Book Club Associates. p. 75. CN9613.
Webb, Brian (1982). The Deltic Locomotives of British Rail. David & Charles. ISBN 9780715381106.