Hello,
The Royal Engineers had a long association with mainly light railway systems stretching back to the late 1880s. THey were active in most British campaigns and much of the process of developing key areas. India and Egypt were big areas for these companies; and they rapidly expanded during WW1, especially in France and Flanders but also, for example, in Palestine.
There is very little written about these activities, however, and the only good book appears to have been written in 1967 and is now long out of print. There are quite a few enthusiast societies and most are on the web. Just type "Light railways" or "military light railways" and you should discover a few, amybe even in your area.
I think the base for these activities would be Longmoor in Hampshire, but again there is little readily available. The RE musueum in Chatham might be able to help, but it is short-staffed and under-funded I believe. If you can get to Chatham that might speed things up a bit.
Hope this helps,
Cholton