If so, this precedent has existed for many decades in Germany, which has had this law in place and banned two other parties for the same reason over that time.
It hasn't led to the slipperly slope you fear, in Germany or elsewhere. I think people understand that Nazis in Germany are a special circumstance.
As the economic and social situation deteriorates, I see anti-EU sentiment becoming waaaaaaaaay more prevalent than it has been during the 70 years post WW2 period you're on about.
This is hard to understand. The party in power in the UK, the Conservatives, are overtly anti-EU and have called a nationwide referendum on leaving the EU. I don't see anyone talking about banning them or the many leading public figures are coming out for Brexit.
> in case you didnt notice, is conveniently conflated with "populist right wing parties" a la UKIP, FN usw
No, it's may others too, as I pointed out above. The parties you mention are actually populist, right-wing, and often racist and xenophobic nationalists.
> I see ... I see ...
To be clear, those are one person's predictions; nothing like it has happened. If any group is at risk of oppression, it's the Muslims and other minorities against whom many of the parties you list openly advocate discrimination.
It's a little more complicated than that.
The Conservative party is officially in favour of the EU, although not all of its members are. Whilst it has allowed party members to campaign for leaving the EU, it hasn't allowed them to use parliamentary resources to fund or support their campaign.
"Anti-EU" is also a vague term. There's a difference between "we don't mind the EU existing but don't want to be a member" - a typical UK Euro-sceptic view - and "the EU is great in principal but maybe it needs more skulls on its uniform" - a typical neo-Nazi view.
Whilst nobody is suggesting banning people who campaign for "brexit" - it would be odd considering we're having a referendum on it - it's worth noting that the UK has not, in living memory, attempted to subjugate all of Europe under its ruthless mass-murdering rule. Given their past, German sensibilities may not be as receptive to the idea of wanting to change Germany's position in Europe, and parties which adopt policies of that ilk may be viewed with deep suspicion.
> it's worth noting that the UK has not, in living memory, attempted to subjugate all of Europe under its ruthless mass-murdering rule
I agree with this point but would like to add a tangential one: The UK didn't do that in Europe, but they did it many other places around the world, as did other world powers. Why is murderous oppression acceptable in Rhodesia/Zimbabwe but not in Poland or England?
Amongst people who think it is, there are basically two reasons:
1. Africa is where brown people live.
2. We (in the UK) tend to have a romantic rose-tinted view of how the British Empire treated its colonies. We imagine that our rule was a net positive for the countries we occupied, bringing civilization to primitive tribes. One of the effects of losing the war is that the German people weren't allowed to forgot the atrocities of Nazi Germany. We, on the other hand, were allowed to forget our own atrocities.
Just adding to your excellent points: The words net positive are used to justify almost every attrocity in history, including Hitler, Stalin, Mao ... torture by the US government (not comparable to those three but the same rationale) ... etc. etc. You have to break a few eggs to make an omlette, as they say.
Speaking of oppressing muslims, for a government that fully supports the ethnic cleansing policy implemented by the Likud (which let's face it, makes the platform of any european right-wing party pretty mild in comparison), the German .gov sure seems to have peculiar standards of what is morally acceptable for a political party to do or think...