Neil Addison of New Bailey Chambers (the man behind www.harassmentaw.co.uk) has emailed me to point out an important amendment to the Employment Equality (Religion or Belief) Regulations 2003, which is due to take effect on 30th April 2007.
Section 77 of the Equality Act 2006 amends the Regulations so as to replace the definition of 'religion or belief' (previously "any religion, religious belief or similar philosophical belief") with "any religion, or religious or philosophical belief".
The important bit is the removal of the word 'similar'. This was previously interpreted in Baggs v Fudge (the BNP member who claimed facism was a 'similar philosophical belief') as requiring that the philosophical belief be similar in nature to a religious belief (so Mr Baggs' claim was struck out).
Thus this amendment re-opens the question of whether political belief can fall within the 2003 Regulations. In fact, during debate in the House of Lords, it was suggested that a philosophical belief should cover a "world view or life stance". Whilst it's harder to think of a more opaque definition, I suspect that would cover fundamental political beliefs.