Any recorded information including, drafts, emails, notes taken, cctv recordings, recorded telephone conversations and all minutes of decision making council meetings. £100k seems a lot and it is assumed to be the cost of the project not what the PC is financing as they are the landlord and must have looked into how much the return to the council would make this a beneficial scheme to the community. Also why would the council make payments towards a business venture anyway?
As far as your allotment holders are concerned the council only has an obligation to meet the needs of the communities desire for allotments and as part of the "move" proposal they are in a good position to have their needs met regarding desirability of new or improved facilities and ground fertility as compensation. (new buildings, water supply, recycling facilities etc.).
So, higher income to the council and improved allotments to the community could be a win win situation looked at from a different informed perspective.