The British Railways Standard Class 5MT 4-6-0 is one of the 12 standard classes of steam locomotive built by British Railways in the 1950s. It was essentially a development of the LMS Stanier Class 5 4-6-0 ("Black Five") which had been the most successful mixed-traffic type in Great Britain.

A new set of 'standard' locomotives was to be built by British Railways, based on LMS designs and incorporating modern ideas. In particular, the Standard design incorporated features designed to make disposal of the engine after a working "turn" easier: a self-cleaning smokebox and a rocking grate removed the necessity for crews to undertake dirty and strenuous duties at the end of a long shift. This was a necessary investment with the ever-increasing costs of labour following the Second World War.

The original design proposal for the class 5 locomotive had a 4-6-2 wheel arrangement, similar in concept to the Bulleid Light Pacifics that performed impressively during the 1948 Locomotive Exchanges. However, this was deemed unnecessarily large and costly for a class 5 power requirement, so the successful LMS Class 5 4-6-0 design was used as the basis instead. 

A total of 172 were built between 1951 and 1957. 5 have been preserved.