In a Parliamentary system, you win a seat if enough people in one constituency like you. If the US had a similar system, the 'Fuck NYC' party might win upstate New York. In the UK, such local parties include the SNP in Scotland, the Liberal Democrats in southern England, SF and the DUP in Northern Ireland, and PC in Wales. None of them can win across the UK, but they often end up as kingmakers if neither of the big parties can get a majority. If that happens, they can then demand some benefits for the regions they represent.