I have to say that I don't think the Joint Statement of the Archbishops of Canterbury and York is the best way to tackle the British National Party.
The reason is a British establishment institution telling individuals how to vote, especially of course working class voters who might desert Labour for the BNP who are not exactly first listeners to the Church of England. There are two reasons, the first being establishment institutions are not exactly well regarded at the moment, and secondly the Church of England in particular is kept at arms length by most of the British public.
Also the question is whether the public need reminding. There is something condescending about the institution 'having to remind the public' as if the public does not know already. People would vote for the BNP precisely to give politicians a kick. It is a dangerous way to do it, but an establishment saying don't do it is likely to get people to do it. Plus thanks for the publicity, says the BNP able to play the martyr card.
However, had Dr John Sentamu said this himself, and said it as an individual, then this would have been different. Then the public as individual voters would have identified with an individual. John Sentamu is black, and a target of the BNP, and this would bring it home. Then it is not about an institution, but about a real person, and so instead of using the BNP to kick institutions that have become corrupted, there would have to be overt racism to so vote BNP in order to attack John Sentamu.
It is not a criticism of Rowan Williams. He might not be regarded highly within Anglicanism at present, as an example himself of arguably working the institution and wheeler dealing, but most folk haven't a clue about how Anglicanism operates (better keep it that way, perhaps). Also this statement comes on the back of another one from Rowan Williams about stopping exposing of MPs, when the public want MPs to be exposed further and clear them out. He has misunderstood the public mood or the public purpose rather as the Speaker Michael Martin tried to dodge around it. Rowan Williams on this BNP issue is just the other person. The two of them together is understandably to emphasise the importance of the matter, but I just think it would have been better to have had such a statement (modifed) from someone in the BNP's firing line, to then emphasise what is involved in voting for such an outfit.