Hello
These links contain a few track plans that might help.
http://www.martin.loader.btinternet.co.uk/Fairford.htm
http://www.greatwestern.org.uk/index.htm
Looking through them and also in some of my reference books, it is surprising how few branch lines had any loco facilities at all by the 1930's. for example, all the Midland Railway branchlines in mid-Gloucestershire were served by locos based at Gloucester Horton Road shed. The working timetables all start and end with a loco movement to or from Horton Road.
Nailsworth had a turntable and some carriages appear to have been stabled over night on the branch but no locos.
Hope this helps
Regards
Chris
ps
There used to a thread, possibly started by John Whelan that had lots of useful links and information sources about British Railways but I can't find it any more.