Have you established that the land comprising that over which you have obtained a prescriptive easement is registered to anyone - by asking the LR.
You can do this for a small charge using Form SIM - the procedure is explained in Practice Guide 10 here -
http://www1.landregis...d/documents/pg10.html
You won't be able to use the portal 'Who owns a Property' service as there isn't a postal address for a parcel of land - you will have to describe it in relation to something the LR can relate to - 'land to the east of XYZ etc' and make the application by post.
I suspect that your situation is very common where estates developed as council housing has subsequently been transferred to a social housing provider. The main estates roads are adopted as part of the public highway but the little lanes or alleys that run between people's houses are not necessarily.
When you successfully made the application for an easement, did you provide the LR with a plan showing the area of land over which you were claiming a right to pass/repass? - if so you can use that to describe to the LR what you are now asking whether they have an owner registered.