In any developed country, you are always best to stick to the local regulations if you are doing any kind of electrical or gas installation or even water plumbing.
The biggest and most dangerous problems occur when you install something using assumptions from a foreign (UK in this case) wiring system and connect it to the local system which has completely different assumptions.
Things like fusing, earthing systems, assumptions on earth loop impedance etc are all calculated into the local system's regulations.
In general, any *modern* European system, when wired *to code* is very safe, regardless of which EU country you are in.
I would absolutely never suggest wiring anything outside of the UK to UK wiring regulations as they are extremely odd.
Many a non-British electrician would be as horrified at old British installations as some British expats are at old continental installations. I know a few Germans who nearly keeled over when they saw rewirable fuses, no RCDs and the odd ring main system on old British wiring installations.
I would say if you are concerned, upgrade to modern Bulgarian standards and ensure that RCDs are fitted.