A permissive path is not a public right of way. It is a route that can be used by the public with the permission of the landowner, ie controlled access is granted for a fixed period of time.

The landowner has the duty of care to users of the permitted paths and is responsible for the maintenance of the paths.
Permissive paths are usually the subject of a formal agreement between landowners and the highway authority (Cambridgeshire County Council).

Permissive Access - online map  
The online map on this website shows permissive access provided by Cambridgeshire County Council’s County Farms Estate. The estate has some 300 tenants farming over 13,000 hectares (32,000 acres). 

Public access sites have been created and new permissive footpaths and bridleways.
Some of these routes include new woodlands and others have been entered into the Countryside Stewardship Scheme, and there are now almost 40 schemes in place across the County providing a network of permissive paths.

Anglian Water also provide a network of permissive paths around Grafham Water.