British Railways Driver's Manual - Numbering And Classification Of All BR Locomotives - General Data and Principle Dimensions
Classes 20 - 24 - 25 - 26 - 27 - 31 - 33 - 37 - 40 - 45 - 46 - 47 - 50 - 55.
Issue Date: Unknown   -   BR 33056/10  Issue 2 - Supersedes BR. 33056/10 Issue 1.