As an Englishman born and bred, it is only since leavig England that I've been able to see the narrow-minded insularity and chippiness that seems to colour so much of the national character these days. It would take a latter-day Orwell, and certainly a better polemicist than me, to uncover the root causes of such a decline, but it does seem to be there - as exemplified by the original post.
There seems to be a national passion for whingeing these days. Whatever happens, it's always unfair, we wuz robbed and the glass ain't half empy; it's in shards on the floor.
As such, it's little wonder that the BNP find the English underclass such a fertile recruiting ground for their brand of bigotry and vitriol; their policies are just the 'logical' extension of the arguments of the Mail and the Express, which in turn are the canteen and bar-room whinges of the average Englishman. Blacks, asylum seekers, Jews, Europe, the Scots, the Welsh, Socialists, Political Correctness gone mad - hell whatever's wrong with the country, it's always someone's else's fault!
SNP and Plaid may be nationalist parties, but they don't have the appalling spineless chippiness of the English nationalists. Plaid states that it is the party for for anyone who wants to make Wales their home, and openly boasts of its aim "To build a national community based on equal citizenship, respect for different traditions and cultures and the equal worth of all individuals, whatever their race, nationality, gender, colour, creed, sexuality, age, ability or social background."
Somehow I can't see the BNP having such an aim.
(and the legality argument won't hold water because it is patently absurd)