[see previous posts for details of Smallwoods Association]
'Assuming it's not in a National Park, AONB, SSSI, etc, Martin Glynn from North Yorkshire also agrees that generally speaking sheds in woodlands come under Permitted Development but only if incidental to the management of the wood. Martin recommends reading Planning for Small Rural Businesses which can be accessed from the Royal Town Planning Institute. A further resource is Chapter 7 run by Simon Fairlie. Their DIY planning handbook for smallholders, low impact developers, etc, costs £15 from The Land Is Ours whose Chapter 7 department also offer free advice and publish a quarterly newsletter.'