The graph for Britain is clearly wrong. David Cameron is clearly far-right by any European standard, so the country's swing to the right should be a lot more pronounced.
The far-right in the UK is UKIP and a bunch of Conservatives who are basically UKIP, but don't want to risk losing their seat by jumping ship.
What matters here is where parties and politicians lie compared to the historical norms of their country, and Cameron is far closer to that then, say, Thatcher.