Probably the best way is to check who actually owns what and whether any rights already exist.
Are the titles registered? If so, you can check the title plans at the Land Registry for about �3.00 per title and per plan.
http://www.landregisteronline.gov.uk/
You can check with the local authority if it is official common land ( as in public ownership (http://www.naturenet.net/law/commonland.html( or do you mean just common to both of you?).
For 50 years then I'd say there is a good chance of having accrued a right (though there are criteria though - have you used it without payment, requiring consent, dispute etc...).
Give your local Land Registry a ring and they will be able to point you in the right direction...
http://www1.landregistry.gov.uk/regional/
Do your neighbours use your path also? If you go for a right over theirs then they may do likewise.
Maybe you should just come to some agreement and put it in writing. Avoid a dispute at all costs.
When doing this please bear in mind future use eg if your neighbours change or need different types of access eg larger commercial vehicles or with animals.
Also consider repairs and maintenance and who should pay for what.
Also bear in mind any lender's consent may be required if you are granting rights to other people and similarly for your neighbours. Lenders may ask for a charge for this and may insist on solicitors being used.