This is ridiculous. I just read through two pages of ignorant pontifications.
To be brief, two points will suffice.
1) The position of Chief Rabbi in England is extraordinarily complex. Many spiritual battles are at stake. This is not a matter of halachic precedent. If I would attend a church service and claim that R’ Mirvis did so, that would make me a fraud.
2) We all know (or should know) that there will be a dozen blogs this month on the topic with all types of contradictory information. This isn’t a never before phenomenon. It’s hard to pin down exactly why we do not go into churches.
For those who don’t know, there is a raging war in England for the balance of power among the Jewish factions. They have everything to gain with coming together. Yet, these attempts always get foiled by some fanatics and rabble-rousers. (Some are observant, most are passionately not.) Such is the company this conversation belongs in.