Where Thames Water is the sewerage undertaker and its approval is missing, a retrospective assessment may be possible, but it is not guaranteed and may require evidence or changes to protect the sewer. [1][2]
Check ownership and history before choosing a remedy
A pipe beneath a private garden is not necessarily privately owned. Water UK’s explanation of the 1 October 2011 sewer transfer illustrates how previously private shared sewers and qualifying lateral drains became public assets. This is why the construction date and the asset’s ownership history matter when assessing an older extension. [2]
Do not infer from today’s public-sewer map alone that a particular historic owner breached an agreement requirement. Equally, an absent line on a map is not proof that there is no sewer: Thames Water warns that some assets are not mapped. Ask for the pipe’s position, status and the relevant building history to be established together. [3][2]
Planning permission is not sewer consent
Thames Water’s current guidance identifies building within 3 metres of a public sewer or 1 metre of a public lateral drain as work requiring its agreement. These are the company’s current criteria, not a substitute for checking the circumstances of an older project. Its approval protects the sewer and future access; it is separate from planning permission. [4][3]
Retrieve the original agreement and approved drainage details, then check that they cover what was built. Thames Water advises retaining agreements because they may be needed on a sale. [1]
What a retrospective assessment may involve
Thames Water explains that it may not grant retrospective approval where work has not sufficiently protected its assets. Its published submission requirements include a location plan, drainage layout and section drawings showing the relationship between foundations and the sewer. Further information depends on the construction. [1]
For a retrospective application, Thames Water says to select the retrospective option on its application form. It requires a CCTV or on-site survey for every application class to check whether construction damaged the sewer. Establish the survey arrangements before assuming that old photographs or the building’s age provide enough evidence. [1]
Internal access chambers are a particular issue: Thames Water’s current guidance does not allow manholes inside a building and requires appropriate relocation through its process. Have the actual arrangement reviewed before carrying out alterations to a public asset. [3]
Consider the building-control file as well
An absent water-company agreement can affect completion certification and a later sale. However, resolving building control and obtaining the water company’s position remain separate tasks. Keep the agreement, construction details and relevant statutory certificate together without presenting one as a replacement for the other. [3][5]
Cost, insurance and sale timing
Request a case-specific assessment of application charges, investigations, design work, repairs and making good. A fee for an ordinary proposed build-over is not automatically a quotation for resolving an existing extension. The required evidence and any alterations determine the practical programme. [1]
Have the conveyancer identify any insurance option before discretionary approaches that might affect eligibility. A building-regulations policy is defined by its wording; do not assume it covers a water company’s separate rights. Insurance also does not inspect or repair the sewer. [6][3]
Do not commit to a guaranteed retrospective agreement or sale deadline until the outstanding technical and legal requirements are understood.