I think this is really an unjustified smear on UKIP.
UKIP is a right of centre, somewhat socially conservative but really more libertarian. They are a relatively "small state" party. They also think that key decisions on our agriculture, industry, fishing, taxation etc etc should be taken by our democratically elected representatives in Parliament rather than unelected unaccountable apparatchiks in Brussels. They don't think that this can be achieved while we are in the EU. They gain their support across the political spectrum but I think it's fair to say more from natural (or former) tory voters who feel that the present Conservative party is not really Conservative.
You may agree with them or not but it seems to me that this is a perfectly principled and honourable position to take. (Cameron's abusive description of them as "loonies, fruitcakes and closet racists" will, I believe, come back to haunt him.)
The BNP is a National Socialist/ White Nationalist party. They believe in a racially homogeneous society (which is anyway no longer even a remote possibility), protectionist trade policy, and a number of basically traditionalist left wing policies such as increased old age pensions, a fully funded national health service, and workers' cooperatives. They are a "big state" party which gains its support largely from disaffected natural labour supporters in poor areas, though their claim to be "the labour party your parents voted for" is pushing it. There is clearly a nasty racist core to them - largely I suspect their support consists of bigots and losers.
It seems to me that they are more accurately descibed as a party of the left, not the right.
So I'd put the BNP and UKIP actually at opposite ends of the political spectrum.
By the way I'm not myself a member of UKIP, or indeed any other party.