This is true for a lot of countries. The huge electoral break of the European Far Right in the last few decades is at least partially due to voters who always were there returning to their natural habitat, which they had left when that habitat became too toxic after '45. (I'd say)
I must say I seriously doubt that. I think it might be true in some countries on the continent (like your Belgium or say Austria) but not in Scandinavia. For one thing, the WWII far-right was a lot more right-ish than the current far-right.
I wasn't saying that I knew for a fact that that was the case in Denmark, I don't know enough about the place to make such bold claims. But what matters isn't the real ideological profile of a party, but the perceived one and/or the degree to which a certain relative position on the spectre would still be associated with WWII. In my own case, the VU was way more moderate than the N-VA, yet it is the latter that turned out to have a greater potential base.
But in general, I think it's true for a large part of Western Europe.
