Can you establish your 26 years' use? Any evidence?
If so, you have what is known as a prescriptive right because you have been doing this for at least 20 years.
A right of way/access cannot be blocked. You can get an injunction against the neighbour by going to court (likely that the neighbour will have to pay your costs if you can establish the prescriptive right). Alternatively, you can remove the gate ( this is a self help remedy) but you will have to give the neighbour written notice of your intention to do this. Not much notice is needed.
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