Surely the properties title deeds show the boundary and what you are responsible for by the "T" logo on the deeds
Our house stands on a corner plot, main road to the front, side street to the side. The terrace continues on the other side of the side street. Once upon a time, we owned the land up to halfway across the side street, the other half was owned by the house opposite. This was no more than a track but, when houses were built at the top of the side street, the council needed permission to turn it into a proper street. Both owners at that time obviously did not want to be responsible for repairs to the pavement, roadway or furniture on that street, so signed ownership over to the council.
Now, the point. I'm not exactly sure when this happened, but our deeds show that we still own halfway across the street. Deeds can be out of date and can be challenged by interested parties. Sorry.