It didn't take long. Here is a post on the Christian persecution web pages which sits rather oddly among the other stories of genuine persecution that appear on their pages. Acts which are certainly reprehensible and should be highlighted indeed.
Let me make it quite clear: I think that persecution of anyone is wrong. But Boris Johnson taking some action (which may well turn out to be counter-productive) to ban bus ads produced by an organisation which, despite what they say, offers to cure gay people of their gayness, is understandable and certainly supported by many.
The bus ad issue is moot, and I can't say I have completely made up my mind about it.
Update: this excellent article has helped me to make up my mind!