In reply to no_more_scotch_eggs:
This is all a bit hazy in my memory but IIRC there were definitely a few British Muslim activist who went begging to other countries to get a response particularly after they felt they were ignored here. So ultimately Khomenei probably would have never heard of the book if people here hadn't gone to the Iranian government saying "look! this is terrible isn't it!" On the Sunni-shia split; I think it was that in the UK people who fancied themselves as Muslim community leaders but who HADN'T protested against Rushdie saw the success of those who had, so criticised them by saying they had to go to a Shia country (Iran) to get support, and this made them suspicious. But Iranian moves like this always have to be seen in their efforts to claim a leadership role over Muslims, and particularly their strategic competition with Saudi.
I wrote a long article on the Danish Cartoon Crisis many years ago, and it was funny how much it paralleled the Rushdie affair.