Advice on 610mm sewer under house

[al2023]

Hi, I'm in the middle of buying a house, but found a 610mm diameter public surface sewer lying longitudinally underneath its side extension. The extension is part single and part two storey, so it would be huge loss if Thames Water needs to tear it down for repairing or replacing the sewer, and Thames Water is entitled to do so at homeowner's cost because such a covenant was added to the Deed as part of the build-over agreement. The house was built in 1920-1930s and assumedly the same with the sewer. The solicitor shows little concern, so I'm the only one to look out for myself.
I like the house but am worried about potential risks of the huge sewer. What would you do, pull out or negotiate on price? Thank you.

Think I'd be talking to insurers about this and checking out who is responsible for what, in the event of a failure, as not just the pipe but the resulting damage from sewage too. Worth checking who is responsible for what https://www.citizensadvice.org.uk/consumer/water/sewerage/who-is-responsible-for-repairing-drains-and-sewers/

When was the extension and build over agreement?

Extension and agreement were back in 2004-2005, and Thames Water has always been responsible for the public sewer. But by the agreement and covenant added with the extension, Thames Water is no longer responsible for restoring things back or compensating the owners for the damage during their works. That's where it now causes concerns.

I think it would depend how much I wanted / needed the house! My gut instinct is that I wouldn't want to buy it, but I'm overly cautious by nature.

I think we had this when we bought our previous house. Indemnity insurance covered it - solicitor sorted it out.

Personally I wouldn't take that on unless there was an iron clad (irrevocable) insurance for rebuild.