Since the general sense is that we never go into churches, it would be better not to post sources. As this would only lead to sway readers that it is permitted. [All the sources that something is forbidden, are not as strong as the statement that we just don’t do it.] If you really need sources for this, your just an imperceptible ideological shift from entering a church yourself.
My issue here is not that I am convinced it’s permitted to go into a church in a certain context. I am mildly annoyed that posters who have no idea what any of this is about, are making a stink out of themselves. It’s undermining to their own credibility and objectivity that they keep repeating the same lines without taking a second look at the factors.
Rav Mirvis took a very difficult position and has been blessed with success while keeping a relatively low profile. The Office of the Chief Rabbi is not an halachic institution. However it is more deliberate than any beis din or organization in all of World Jewry. When the daily tasks are akin to carrying lit dynamite sticks, it goes a long way to not being fazed and never getting carried away in the moment. There was no psak given that you or me or anyone can go into the church. What was done is what was understood to be needed.
The rationale that “oh, he is some sort of zionist and not my type” is particularly insulting. So, the Torah is reduced to whether the rabbi involved is your type or not?!? when you learn some gemara, do the statements mentioned also depend on being your type? How can anyone ever pass judgement on anything without a fully understanding what the issues are? The haphazard way some of the strongest proponents of ‘Rabbinic Judaism’ hurl their opinion without checking the facts is very depressing to me… Remember that you are a role model to many that are completely unlearned. Do you want them to also pontificate based on their gut instinct?