I've been in the hobby for close to 30 years all told, though I came out of it for a long while. I started getting back into it in 2015, which is when I became a member on here.
Back in the day, it was mainly coldwater fish I kept, various goldfish and such, but I did have a few successful years at keeping piranha. And yes, over here in the UK pretty much anything goes. There's no real need for harsh legislation when the temps of our UK waterways would kill any aquarium "escapees".
As I mentioned before I have two tanks, a planted 180 with an assortment of smaller fish and an unplanted 360 with my bigger fish in. Prices and availability of fish seem ok in the UK, though I've never asked for anything really rare or exotic.
We do have some beautiful natives though most of them would be better suited to outside ponds. One day I do plan to turn my 360 into a coldwater European perch tank, though that could be many years away yet because my current stock is quite long-lived fish. See pics below of my tanks and the European perch, my favorite fish.
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