I'd say most of them are atheist and have absolutely nothing to do with religion at all.
And I would say they aren't atheist.
What I would say is that they belong to that vast majority in this country that are made up of the unintelligent who lack the willingness to acquire any sort of knowledge beyond what box set they are watching or the latest "offer" Sky TV are pushing at them to keep them in their ignorant apathetic state.
Whether you agree with atheists or not, they have usually thought through their position and in my experience (although I know others claim differently - but if its good enough for them its good enough for me) atheists very seldom express any homophobia.
In addition you might want to look at the institutions that currently support discrimination against homosexuals in this country - that would be, in the main, let me see - oh yes the religious institutions.
They will be the same institutions that in the main have long supported anti gay views within society - and if you scratch the surface of the aforementioned apathetic, ignorant folks I have described, sooner or later they will say well it's in the Bible.
Unthinking, apathetic, caffeine drink addicted, MCdonald eating fuckwits that we have created by our insistence that the market knows best, that consumerism is king, and self interest is the way to go.
The current thinking of Free marketry being created by Thatcher, Blair, Cameron who are or were,at least, nominally Christians.