My BIL and I are close to exchanging contracts on a house that we’re going to tidy up/possibly extend and put back on the market.
Just found out that a small extension they have already built (4 years ago) has no documentation.
Walk, run, use it as a bargaining chip or just carry on regardless?

Get them to pay for an indemnity policy which will pay out if it needs to be rebuilt because of a planning regs issue in the future.

Pretty standard, they’re not expensive

Speak to the local planning officer for advice

solictior should have examined this and sorted out indemity insurance,

What IHN said.

Although they usually have a clause making them void if you tell the council about the extension yourself. I’ve no idea how that would play out if you did some other work that required submitting drawings or having inspectors round.

It was about £200 each for our conservatory (brickwork not tied into the main house), and loft conversion (it’s just a carpeted loft with permanent ladder-staircase and a velux, but the mortgage co got twitchy about it).

I’m not too concerned about planning as it will fall within permitted development but the building regs is an issue so we’re going to chat with our surveyor.

Having been in the exact same situation, unless you can inspect the underlying fabric walk away. Mine was a self built utility room and was demolished with nothing more than a couple of breaker bars and club hammers (to smack the outer skin occasionally) in a couple of hours. Most of it was taken down by hand. As in, pushed over.

….. and the end result was……

We are paying £10k less for the house which will more than cover rebuilding the little extension if required (which I doubt).

Bargain! At least for that discount you can be as invasive as you like and make good.