Approach the council and ask them about it .. in the current financial climate all local councils are thinking of cutting and not spending. and creating an allotment would be spending.
What area are you in (postcode)... as I know of a company who are spreading their wings across the UK, and are always on the lookout for a community project to give themselves a bit of positive local exposure. (they have money and the labour ).
... another alternative ..
http://www.landshare.net/ .. you never know until you ask. You may be surrounded by people who want to share in your area.