The British political and electoral systems are fundamentally broken, to be sure. That said, it's also worth noting that in this case by far the biggest loser at the last general election because of that broken system was UKIP, the "small anti-EU, right-wing party" you mentioned, which despite commanding 12.7% of the popular vote wound up with only 1 MP out of 650. Even the Lib Dems, who took probably the biggest political battering in a generation at that election, didn't lose out that badly.

Had we had anything resembling proportionate representation in the House of Commons after the election, it is not unlikely that UKIP would have held the balance of power in a hung parliament, and that as effectively a single-issue party they would then have demanded action on their main issue as the price of co-operation. Whether any of us would agree with them or not, the fact is that nearly 4 million people did vote for them, so it's hard to argue that the current situation is somehow unjustified.

My personal view is that one good way to bring more accountability into British politics would be to make more use of direct democracy on specific issues, moving away from the transparent fiction that whichever party wound up in power despite almost always receiving a minority of the popular vote somehow has a popular mandate to implement any policy that was in their manifesto on any issue. From that point of view I'm happy to see a referendum that splits party lines take place on such a controversial issue anyway, regardless of my personal preference for its outcome.