In reply to Tom Valentine:
> That doesn't seem to apply to the UK black rat population.
Yes, that's an interesting one. I don't have any problem with rats, in the right places, and would prefer the smaller, less invasive black rat. They now seem to be restricted to offshore islands - they were famously abundant on the Shiant Isles in the Hebrides, but were exterminated there by the RSPB.
I thought black rats used to be regarded a bit like red squirrels - the cuter native species being driven out by the more aggressive recent arrival They get a page on the People's Trust for Endangered Wildlife*, for instance. Interestingly, the RSPB carefully 'other' them as as 'non-native', although they've been here since at least Roman times (so much longer than rabbits).
* I have my doubts about them as an impartial source, though. They seem to think that it was gerbils that spread the Black Death but I doubt they were responsible for the Great Plague in 1665, unless our pet keeping habits were rather different from how I imagine 17th Century London.