BR Stationary Supplies number - a lot were just progessive numbers issued on a "next one" basis, with sub divisions for similar items. The Clerk at any depot or station who did the periodic stationary order to the BR Stationary Stores at Wistaston Road, Crewe was the person to get on the right side of and in the bigger offices he would have some kind of catalogue. The stationary used to arrive in wicker hampers and this event was always eagerly awaited by the clerks.
As an example of numbers used, most BR clerks would have a BR 3/6 memo pad for writing letters, a BR 5/3 pad for jotting down telephone messages or a BR 20145 multi use pad on which you ticked a box to send simple messages such as "please reply to my letter of". 12 inch rulers were BR 1480/2 and at one time litter baskets were BR 6/1, hence the old instruction to "file it in 6/1"!
For years the one thing you couldn't get was Tipp-Ex. BR had glass jars of "white-out" which came with a brush down the middle - horrible stuff. When I was at the Divisional Office at KX in the 1970's you were supposed to use "white-out" but we used to go a few doors down the road to a stationers, get some Tipp-Ex (and in those days Tipp-Ex thinner - there was some serious sniff with that stuff - whoa!) and he would ring it up as batteries, which our stationary stores didn't stock and, on producing the receipt, we would get petty cash for!