British Railways coach designations were a series of letter-codes used to identify different types of coaches, both passenger carrying and non-passenger carrying stock (NPCS).
Their codes were an acronym of their traditional railway description, e.g. GUV for General Utility Vans.
Suffix codes Y or Z are not shown, as these could apply to variants of any or all vehicle types.
The original Second was more or less abolished in the 1870s as a result of the Railway Regulation Act 1844, remaining only in limited use for special services, such as those meeting ships (which retained the three-class system from which railway classifications had originated).
[3] Multiple unit coaches originally distinguished between open and corridor types by adding the letter O or K at the end (for example, TSO or TSK), and also distinguished coaches with lavatories by adding the letter L at the end (for example DMBSOL) but these fell out of use when corridor stock became less common which enabled the codes to be restricted to no more than four letters.