Thanks for your reply.
The law concerning this states that where a party uses a right of way, WITHOUT the express consent of the owner of the land, for 20 years or more, and this right is exercised without dispute, that party has acquired what is called "a right by prescription". This means the party has acquired a right to continue to use the right of way automativcally, without the need for registering any such right at the Land Registry (although this is preferable, so as to avoid any argument in the future).
Therefore, you need to satisfy yourselves, via your Solicitor, whether any such right has been acquired. It may well have been that if the previous owner consented to the neighbour using the right of way, this would have been classed as a mere "Licence", meaning that this agreement could be terminated by either party giving notice to the other, and the 20 year rule would not apply as consent had been granted.
Either way, a simple letter signed by the neighbour confirming that no legal right has been acquired by him would be sufficent evidence and adequate comfort for you.
I hope this helps and sets out the legal position.
Please let me know if I can be of any more assistance.