It depends on what the, wel,l deeds say
you are almost certainly in an area that is covered by the Land Registry
and it depends on what the entry says
they should have told you in pre-sale questions
and finally the only right they could enforce which is not recorded in the LR are those which are visible on inspection and from what you say - it wasnt.
but you need the advice of the person lawyer who acted for you in the purchase including the question if were true - why werent you told, especially as it would have been a deal-breaker
This type of question is not uncommon after in-fill building.