NSALG sought Counsel’s Opinion on this issue, and is delighted to say that Counsel has confirmed the opinion of the Secretary and Chairman; and confirmed the opinion of the Legal Consultant that the Crowborough case is authority for the premiss:

Planning Permission is NOT required for sheds, and/or greenhouses on an allotment plot!  Please note: a shed or greenhouse over the standard size of 8 x 6 (available from most garden and DIY centres) that require foundations or are connected to services, might be construed as a permanent structure.