If you want to open an allotment site youself on the land then you need to get the land owner's permission for starters.
Is the area within a parish? The parish council have extensive powers and duties to create new allotment sites. They have a duty to provide allotments if there is a duty, and they have wide powers to lease or buy land for allotments. If it's open land it may already be owned by the parish.
If you don't know who owns it you can use the
Land Registry search which costs about £5.00.
Creating a new site is relatively simple. There's never a need for planning permission because allotments is never "development".