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Provided you have been using the access/door continously for 20 years or more, without diispute, hindrance or the express consent of the neighbours over the years, then you have acquired what is called "an easement by prescription", meaning that you have acquired a legal right to continue to use the access.
If, over the years, the several neighbours have just "turned a blind eye" to you using the access, then this does NOT count as express consent and likewise the fact that the new neighbour is disputing your use, does not affect the right that you have now acquired.
Although you have automatically acquired the right, and nothing further needs to be done, it is best for you to make a formal application to the Land Registry, so that your right can be registered on your Deeds and your neighbours Deeds. A local Solicitor will be able to assist you in making the Land Registry application- you will need to sign a Statement confirming your use of the years. Provided your ap
plication is successful (and I can see no reason why it wouldn't be, from what you have told me), your right will be documneted and any Buyer of your property will also have the right, as such rights "attach to the land" rather than being personal to the individual (ie you).
I hope this assists you and sets out the legal position.
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