The issue isn't just about a party getting into power. Having a single candidate win adds credibility and influence to the party. They cannot be denied access to facilities, and have to be treated equally in terms of the benefits and privileges afforded to holders of that office.
And how much credibility did BNP get? Where are the BNP now?
Not so. With PR it is likely that coalition politics will be more common. In that situation a minor party can play 'kingmaker' and extract a very large price for doing so. I'd suggest the DUP in 2017 is a good example where just 10 MPs made all the difference, and had a disproportional impact on policy making.
Because of FPTP, the Conservatives had very little choice of parties to work with. In countries with PR you are more likely to get a rainbow of parties elected where you are more likely to find a coalition partner that you can work with. For example, it is common in the Netherlands and Germany to have "grand coalitions" of the major centre-left and centre-right parties.
There is obviously dissatisfaction with the FPTP system and there are many people like me who crave a fairer system. Are there many voters who lament having a PR system and wish they had the British or American system? Probably not as many. If PR is unsuitable for the UK parliament, why is it fine for the Scottish Parliament and for the Welsh and London Assemblies?

