I live in dense, back to back, terraced housing. The house was built in 1903, over a sewer it transpires. There are no extensions, just the original house.
We are selling and the buyer's solicitors is demanding an indemnity as there is no buildover agreement, which didn't even exist in those days. They have informed the mortgage lender so we can't refuse unless we want to cancel the sale.
I am so cross and concerned that this is going to cost us a fortune. All the bloody streets in my local area must be over sewers and no one has bothered about this (for my house anyway) for 110 years!
I got this sort of indemnity when I bought my house as the seller didn't have it. My conservatory is built over main drains. The indemnity cost about £40. I wouldn't worry. Your solicitor should get a quote for you.