This is the bible on British Army Trade and Proficency Badges and as you can see very expensive but you can normally find them for about half of this if you watch out on e-bay or the British Military Badge Forum.
https://www.ebay.co.uk/itm/353720920...iABEgJJTfD_BwE
The problem with the trade badges in both world wars was that there were many unoffical badges / colour combinations in use the purpose of some is not now known. The Canadian Army also had some of its own badges not used by us including Telegragh Pole and Valve (or Light bulb).
I have one of the biggest trade badge collection in the UK if anyone want to see what signals related badges I have.