This is the place to discuss not just allotments but all general gardening problems and queries which don't fit into the specific categories below.
(formerly allotments and tips, hints and problems)
Check out Patrick Whitefield's book - I opted for an edible hedge but am turning our orchard into a forest gardening with a bit of help from the Martin at the Agroforesty Research Trust.
http://www.farminmypocket.co.uk - polytunnel offers, reviews, and more self-sufficiency information than you can shake a chicken at