These are the figures quoted by David Keen
This data from the Church Society (source) also seems useful:
And this one confirms it:
We can add to this the expected rapid decline in clergy numbers over the next ten years (as the baby boomers retire and aren't replaced) and the way that this links in with the increasing age profile of attenders (and what this means in terms of a sudden drop for actuarial reasons). See also David Keen's post on Diocesan growth here.
"One of our problems may be that decline is so slow and imperceptible that we don’t really see it coming clearly enough. I have seen large companies perfectly and impeccably manage themselves into failure. Every step along the road has been well done. Every account is neatly signed off... I sometimes feel the Church is a bit like that. I wish that all of us would have a sense of real crisis about this."
(Andreas Whittam Smith)
The Lord being my helper I expect to be working for the church