To answer your question without having to wade through all the OT traffic
polluting the thread...

Yes, herons (and almost all wild birds) are a protected species in UK. Not
only that, but it's illegal for private individuals to own any firearm
(which includes shotguns) so predators (non-human) can only be deterred by
passive means.

I, too, had my pond cleaned out by a heron. I grew up in farming country
where shotguns were part of life (for rats, rabbiting, etc). Nearly 50 years
ago, a friend aged 14 accidentally shot/killed another friend, climbing over
a stile and fell, gun in hand, whilst rabbiting.

Deterrance, not extermination, is the civilised solution. "Final" solutions
have potential for disaster.

Sincerely, Len