I believe European nations follow similar rules. The system is two tiered.
Lower end is a gun that does not require a license, or in Britain, a Fire Arms Certificate (FAC). Guns that do not require an FAC are limited to 12 FPE. Not sure why they chose that, but 12 FPE it is.
To go over 12 FPE, you need a FAC, and once you have an FAC, you can go to the higher power levels.
Yup, 12 fpe isn't much by US standards, but they do a lot of small game hunting with it, so it must work!
It's also one reason why most European non-FAC guns are .177 to allow extra velocity under the 12 FPE limit. On the good side, they use less air per shot, so something like the Maximus gets max 30 shots in full power, but around 50 or 60 in 12 FPE power range. Great for those of us that like high shot rates.