I don't know whether buildersmate can understand your question now, but I certainly can't!
Do you mean:-
1. There is an easement over the property in favour of a third party; and
2. The present owners have carried out a development without consent which interferes with the use of this easement?
If that is the case, then:-
a) I don't understand your ref. to an insurer unless it relates to a defective title indemnity insurance. If that is the case, then it is something the present owners should be arranging and pay for, but which you have the benefit of should anyone come along and want to use the (now unusable) easement; &
b) I don't know why you are being asked to sign anything about this - it should all be sorted so that you take the property with a clear title and no possibility of this problem coming back to bite you later on - or causing difficulty when you come to sell; &
c) You should insist your solicitor advises you properly in writing on all this. If he doesn't, then use his firm's complaints procedure; &
d) Don't go ahead with the purchase until this is sorted out. Otherwise you could end up with a significant liability if the easement had to be re-instated.
If my surmising about the situation is wrong, do post something in more detail to explain it.