They responded to my email this morning saying 'its not ours', check with Land Registry.
To which i told them, i have and the property plans/deeds do not mention the bordering fence. I then asked, if you are certain the fence is not yours, can you provide the boundary details you have that confirms this, so the home owner can be approached and made aware of the maintenance to be done.
Turns out they now need to check this and come back to me . . . . .
Funny how they change their tune when you call them out with the information.