I never settled a disputed debt from when I lived in Switzerland, and I do wonder if I'll get pulled up the next time my passport is inspected at a Swiss border control. It was 24 years ago now, so I'm hoping the statute of limitations will mean I'm in the clear soon.
I went to Switzerland with someone who had a speeding find from 2 years before - they were stopped at the border but it was pretty straight forward just to pay it and they were let in.
I think they can chase you for it in the UK. Also they may remember it at passport control when you go there in the future