I am buying a house that has an extension. The extension was built in the 1970s and had planning permission. The drainage search has revealed it is built over a public sewer. This public sewer serves this property and 3 others, and would have been classified as a private sewer prior to the law change in October 2011, when it transferred ownership to the water company.

All advice online relating to the 2011 transfer seems to point towards the future extensions on properties now being more likely to need permission from the water company. But surely there are many thousands of cases like this, where a previous owner has extended over their own drain, and that drain has now been classed as a public sewer needing permission to be built over?!

Does anyone know if there is any kind of retrospective action the water authority can take, or did the transfer take place on the understanding that extensions prior to October 2011 would not have needed this permission?