Green Belt Architects
If you are asking "What can I do with Green Belt land?", then what you need to find are Green Belt architects and planners who have spent years getting to grips with the policies that set out what you can and can't build on the land on the edges of London, Bournemouth, Bristol, Oxford, Cambridge, Birmingham, Coventry and Wolverhampton, Nottingham and Derby, Stoke-on-Trent, Manchester, Stockport, Bolton and Wigan, Liverpool, Southport, Blackpool and the Wirral, Leeds, Bradford, Huddersfield and Wakefield, York, and Newcastle, Sunderland and Durham.
You should work with architects, planners and urban designers who understand the Green Belt purposes and the all-important Green Belt exceptions - the circumstances when the general rule that councils should consider "construction of new buildings as inappropriate in the Green Belt" does not apply, and could offer a way forward even if your land does not fit into one of those categories.