If you own your home you may not have your title deeds as they will probably be stored by the solicitors who did the conveyancing or your lender if you had a charge over the property.
When did you buy it? if recently then your soicitors may have sent you a copy of the Completion of Registration document (sent to them by the Land Registry). if not they may be able to send you a copy depending on their archive system.
You could also check what they sent you when you bought as they may have sent you copies of title documents which could contain the relevant info. if your property is subj to a right of way you should have been advised.
Otherwise if you click here...
http://www.landregisteronline.gov.uk/ and put in your neighbour's housename and postcode (www.royalmail.com) you can get a copy of their title register if the property is registered at the Land Registry. The info may be on there or there may be reference to rights of way and reference to a document eg 1999 conveyance/lease/transfer/deed. You can also obtain a copy of that document. There are fees but they're not much.
The right of way, if any, may be qualified eg on foot only or on reasonable notice, that they should contribute on the upkeep etc... They may be able to authorise others to use it but it should be reasonable.
Copies of the title plans are also useful as often the extent of the land which is subject to the right of way is coloured on it.
If you can't find any written evidence on a right of way take care as there may not be one and they may have accrued what are called prescriptive rights which can come into existence and sometimes be enforced when something has been done for a significant period of time.
Even if they have not accrued a right yet they may be on their way to doing so especially with you letting them.