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Thanks for answering. We've made a bit of leeway today.
Until we done this, we had one space only, and everyone else had 2. We've found some of our documents today, there's talk of various covenants and easements, but none regarding this issue, so it would seem it was never made legal when the land was registered. Remembering we paid extra for legal cover on the home insurance, my husband phoned today and we've been told that we can basically do what we like with it as it's ours, and it's up to others to contest rather than us prove, unless others start using it. The neighbours in question are the only ones who think they have right to it, and have been out taking pictures and talking loudly about us just trying to increase the value of our house at their expense. It's on the outskirts of a small town, not central London!