One of the reasons may be the church's too close association with the state. The Church of England is the official state church. The Prime Minister and the Queen have a hand in naming its bishops.
The real reason for the decline of the church in Britain is that it has lost its first love and primary message. This came home to me the year that Princess Diana died. I was over there at the time. The clergy interviewed by the BBC talked about her fame and beauty, but nothing about God and death and how we should all be prepared for it. If you lose your message, people won't want to come to hear a boring sermon full of things about the environment, or politics, or anything else but the salvation message and discipleship. It isn't complicated. I'm Cal Thomas in Washington.