A lot of sightings started at the end of the 70s, which would align with the introduction of this law:
https://en.wikipedia.org/wiki/Dangerous_Wild_Animals_Act_197...
Rumour has it that lots of wealthy people simply released their "pets" into the wild rather than confirming with the laws!
Fairly certain there were documented cases of servants confirming this too.
They’re not as charismatic, but they are native, and would be handy in regrowing native woodlands in Scotland.