Ethno-Nationalism is a term coined by BNP leader Nick Griffin to dress up his racist policies so they will be more appealing to a larger electoral population of idiots who think "Ooh, ethno-nationalism, sounds interesting! I'll vote BNP and think about what that actually means later."
Ethno nationalism is a form of Fascism or borderline fascism as contrasted to civic nationalism as practised by for example the Scottish National party. Civic nationalist parties want to persuade everyone who lives in their arbitrary "homeland" to support their claims to independence or whatever it is that nationalists might want, regardless of their race religion or language; Whilst ethno nationalists only want support from people whose ancestors invaded the area before the arrival of whatever religious or ethnic minority they are trying to stir up prejudism against.
Hence it is perfectly possible to encounter a Sikh SNP politician in Scotland, but all BNP politicians claim descent from illegal immigrants who came to England with William the Conqueror, Hengist and Horsa or in Viking longboats.