A quick spot of googling found him... Ian Mitchell and the book was called The Isles of the West. As I say it was an interesting read, even if I was a little wary of the agenda he laid out...
I might try and get hold of a copy of that. Sounds most interesting. The R.S.P.B does tend to polarise people. One one hand anyone who protects swathes of countryside/habitat from ruination/development can't be all bad, yet on the other hand, their stance on eagle owls in GB left me bewildered. I'm no longer a member as their reserves are just far too busy these days and I don't visit them often enough. Besides, membership is pricey.
In terms of the global status of the corncrake, as far as I am aware, they are declining across their range, in some places faster than others, due to ever intensifying farming behaviours to feed an ever growing global population. I think the decline here in GB has been alarmingly fast though as they have no room to 'spread out' and move the same as they might in a larger continental area. I suspect periods of drought in sub Saharan Africa hasn't helped their cause either.
Cheers for the book heads up.
Regards, Chris