I am more worried about the drift to the right in the rest of Europe, where the mood is fearful, anti-immigrant, anti-Islam and deeply hostile to the left. Europe clearly feels embattled because of factors such as terrorism and the rise of China, and has been moving to the right for some time.
The decency of the Brits will win through
I cannot imagine what cataclysm would have to happen for a far-right party not only to be able to grow but to win power in the UK. This is an extremely old country with old mores, and the great rump of the people are not going to be attracted by a far-right party. What we have seen is the sort of protest vote that often happens midterm, and it won't occur at the general election, when real power is at stake.