Discussion boards are almost the lowest form of life on WP:RS, only just above comments sections on blogs.  However if you can demonstrate that GLF has written this (and the fact that it has appeared under his name on a forum that he has moderating rights on may indicate this - although he does not use a "stared" account which means it could be an imposter).  The Daily Mirror account seems to be totally derivative of the Guardian, and the Guardian does not say that GLF was a member of the BNP - just that their journalist contacted him and he said that he could not be active.  The Daily Mirror could well have lost the subtelty of what the Guardian said - I wouldn't like to be their libel lawyer on that!  
With all of this, and knowing GLF's propensity to sue I am going to cut this out.  The fact that the CDA is to the right of the Conservative Party is pretty well established in the article.