Extending over drain - implications?

[PaleGreenAndBrightOrange]

Hi all!

I am buying a house with a side return that I’d like to extend into.
However the survey has come back with a drain issue that might impact my plans. I’d love to know if anyone has any knowledge of this. What are the implications? Will the water board likely approve my plans? Will I have to relocate the drains/access to drains? What would this cost? Would it be worth it?

Issues:
It’s an end of terrace so apparently this means that the drains technically only serve the house I’m buying - not the whole terrace and are therefore classified as private. I’m guessing this means I’d be liable for any repairs and maintenance. Side note - should I get a cctv drains survey?

There is a long drain (see red line) that runs down the side return and also access points to the drains (I believe they are located at the blue cross). See attached pic for details.

Any info gratefully received!

Is this a drain or just an access hatch?

We are also end of terrace and have had to relocate an access hatch, not overly complicated from memory - the water company are still liable for repairs I believe. One can apply for a build over agreement, which does what it says on the tin, if there is no other solution but we didn’t need to go down that route in the end.

We had a similar issue with our extension. You will need to get a build over agreement from the water board. The main thing is if it's a main drain they would likely want to be able to have access (or smash through your floor to get it) so you may need to create some access route within your plans.

Thames Water have some good, clear guidance: www.thameswater.co.uk/help/home-improvements/building-near-pipes

Thanks!