It's not just the CofE that's in rapid decline. Organised religion in Western Europe as a whole is going the same way.
It's the developing world that keeps it ticking over.
In Catholic France they can't fill the priesthood seminaries and are importing North Africans.
In the UK Pentecostal churches have overtaken Methodists in the "bums on pews" stakes.
The total membership of *All* denominations is now under 10% and will halve again in the next 35 years
http://www.ekklesia.co.uk/content/news_syndica tion/article_05095cro.shtml
It's remarkable when the country has special protection for religous education whereas in the US where religious education is legally banned in public schools church attendance is so strong.