Hi Clive,
To add a few more of these numbers from manuals, 100/FW1B was a maintenance manual for an AEC Matador, FW coming from FWD, a company that developed the 4x4 design used on the Mat. FW was used as the VAOS code for AEC right though until recent times. Others seen on manuals, HL for Hillman, HR for Humber, SL for Scammell, BC for BSA motorcycles, all these seem to follow through on to VAOS codes.
ML was for Morris Commercial, I think that Morris cars and light utilities came under MM for Morris Motors.
On Bedford books, the TS number is the companies own code for technical manuals, not just used for government vehicles, and they used PS for parts catalogues.