Was reading through your post, finding it difficult to find fault with anything you were saying, but something wasn't sitting right. And then ...

> I'm certain it's worked well in other countries

It has! In the Netherlands for example, it's just an incredibly convenient system, and if there's anything dodgy going on I'm not aware of it.

So what makes the UK so different to the Netherlands? Genuine question, because I really don't know. My only guess is that the people of the Netherlands hold their politicians to account, whereas nothing ever seems to happen to UK politicians whose corruption is so severe that they're sometimes literally criminal.

It's the difference between proportional voting vs winner takes it all. In the latter case you can't really hold politicians accountable, as you will have to choose between effectively throwing your vote away or voting for the one opposition candidate, that often will be just as bad.

While the UK have some level of representativeness, each circuit has a winner takes it all structure, making change quite hard to achieve on a larger scale.