You would have been required to complete a Sellers Property Information Form TA6 when selling and that w ould be sent to the buyers sols.
here here are some notes and a link to the form which you can download.
the form has been updated and now includes, as the link says, changes in relation to Japanese knotweed, floods, radon, and septic tanks.
The form is colloquially known as a SPIF in the legal profession.
However prior to the update, those queries were in separate forms and if for example there was a septic tank the solicitor would have sent out a separate septic tank questionnaire or rather should have done.
You are not required to volunteer any information but you have to disclose honestly the answers to any questions which are specifically asked.
The form has grown exponentially over the years to include matters which have caused disputes. Some solicitors also have additional enquiries further to these. It has various sections, but summarising them,
1 Boundaries, including who has control any which have moved.
2 Disputes & Complaints including anything which is has been or likely to become a complaint
3 Notices & Proposals
4 Alterations, planning & building control
5 Guarantees and warranties
6 Insurance including claims and anything likely to become a dispute
7 Environmental matters including radon, flooding, septic tanks and Japanese knotweed.
8 Rights & informal arrangements such as anyone else who has rights over the property or whether this property has rights over anybody else’s
10 Other changes
13 Connections to utilities.
14 Transaction information.
You would need to look at the form in detail at each question and also your replies.
Note specifically question number 2 so if you are selling I would be inclined to keep quiet about this. Particularly if you are selling because it could indeed screw up a sale. If you have already complained then the property good will be sold before it got to court depending on what you actually want to happen