Best thing to do is have a look on the Ordnance Survey Map 1:50,000 Landranger for BOAT's and ORPA's - those terms explained here
Failing having an OS map, have a look here
The above will only show you where the lanes are - you will still need to contact the local councils Rights Of Way office to verify theire legitimacy (they might be closed)
The Green Lane Associaiton website should give you some more information.
Lawrence




