Earlier quoted context omitted.
I struggle to see why it is they're simply hate speech and not a valid political movement. A quick look at their "No More Mosques!" campaign should suffice to provide the insight you seek.
Explain to me why that is not something people can vote on? What if I don't want Saudi funded mosques in particular, is there any nuance allowed. There is no racism or exclusion based on a person's ethnicity here. Should we lock up Richard Dawkins for being anti catholic?
If you say that Saudi funding churches, businesses, housing, etc. is not good for Britain for a reason other than you have something against Saudis as a people then you're fine.
If you say you're against all churches because you're an anti-theist then you're fine.
There is absolutely exclusion based on ethnicity. It's extremely important to recognize that there is a difference between someone who is religiously Muslim and ethnically Muslim -- same with Judaism -- and same with Christianity too as well but we don't call it that because we're the default in the West. Saying there is no such thing ignores the dominating cultural impact of religious institutions.