Sounds like a similar case to when we had the garage built.

When our house was built the land at the side was communal, as the kids used to use our gable end as footy nets we got abit pissed off, so put a small fence around and maintained the grassed area.
The way I got told this by the Land registry in Lytham and the easiest way for me to explain on here is ...
If you adopt and maintain communal council land for a substained period of time you can then automatically lay claim to that land.

So if the previous owner has 'adopted' the second space then the property has claimed it, If the land registry documents show this then get the solicitor to sort it at their end.