I suppose it depends on the degree of political difference. It's not too difficult to share a stage with the occasional old-fashioned "one-nation" Tory but quite another to have to spend any time in the company of anyone allied to an outright racist organization like BNP. Bizarrely, the one musician I know who is involved in this odious party used to make his living singing SOUL music. Somehow he didn't see the irony in his performing all the songs of Marvin Gaye, Stevie Wonder, et al and then campaigning to keep immigrants out of the country! However, his band (which included 2nd generation British Asians and West Indians) did see the problem, and left. Can't really blame them, can you?