But if you used a BNP pamphlet or website as a source of information on the British Labour Party, for example, you'd be using it as a secondary source.
We report facts and facts about opinions. The BNP website is a primary source for information about statements about the Labour party made by the BNP. It is not an adequate source for statements about the Labour Party. Thus: "BNP's Nottingham organiser Ray Pootly claimed that the local Labour council had been giving preferential treatment to asylum seekers seeking housing in the area." In this instance it would be good to cite an article by Ray Pootly on the BNP site. It's a factual statement about an opinion expressed by Ray Pootly, who is stated as a matter of fact to be a BNP organiser. The cite supports both facts. "Nottingham's Labour-dominated council gave precedence on the housing queue to homeless people if they were asylum seekers" is a factual statement that cannot be supported adequately by the cite. You would have to find a description produced by Nottingham council in which it described its allocation of housing to applicants (you might also want to support the statement that Nottingham Council is Labour-dominated) or else attribute the opinion to a third party (Ray Pootly or whoever).