Back in the 70s-80s the standard ruleset was the Wargames Research Group 1850-75(?) for modern, and their 1925-50 set for WW2.
Now available from WRG as a PDF:
http://www.wrg.me.uk/WRG.net/History/OLDWRG/Modern.pdf
http://www.wrg.me.uk/WRG.net/History/OLDWRG/WWII.pdf
Unlike
most WRG rule sets, these were fairly concise, understandable and quick and easy to play. Simplistic even - just basic classes, not cm of armour. The emphasis was on tactics, and a playable battalion level game in an evening, and they actually worked very well at that.
The replacement rule sets by them in the later 80s were "WRG standard" (verbose, long confusing run-on paragraphs) and some strange ideas in them. They didn't catch on.
The rule sets that replaced WRG in the UK nationals, and the World Team Championships (late 80s?) were Tabletop Game's "Challenger" for modern, and "Firefly" for WW2. What replaced them I have no idea.