Subsidence ???

[Apple23]

My house has been sold, subject to contract, since October (a cash purchaser if that's relevant). My solicitor has said since before Christmas that we're ready to exchange, but waiting for the buyer's solicitor, who has come back a couple of times with questions.

Estate agent phoned this evening to say that buyer wants me to have a Subsidence survey (is that even a thing?) done due to “the underpinning” on the house.

I've lived here 10 years and not had any subsidence or underpinning, and it didn't come up on searches done when I bought the house.

I grew up in a (Council) house with subsidence. There's no cracking here, corners are square, floors not sloping. Are there anything other visible clues that I could have missed, that would point to there being subsidence? If it had been underpinned, would there be any visible signs? Wouldn’t any underpinning be certified and I'd have had that certificate when I purchased? So many questions...

I'm stunned. I've asked Estate Agent to double-check that they and the solicitor have both got the right property and they said they would send me what information they have.

Apparently, the buyer wants me to pay for a Subsidence survey. Shouldn’t he pay?

I don't have an onward purchase dependant on this sale, but I do want the house gone so I can move on with my life, and it's starting to feel like it's dragging a bit, given there's no chain.

My gut feeling is that something isn’t right, surely the survey would have shown this up months ago? Maybe it's a ploy to drop the price at the last minute?

Any thoughts or advice, please?

I hope someone can come on with some official advice but why would any seller pay for a buyers survey?

If you've got no uneven/sloping floors, no diagonal cracks from the corners of windows or doors, and no unexplained cracks that are horizontal roughly (you can get hairline cracks on plasterboard walls when they are first applied), then they are chancing it.
Ask for their proof that your house has been underpinned as you have no knowledge of it.
Tell them they are welcome to get a survey done, but as your house has no history of subsidence, but you won't be paying for it.
Do you live in the fens or a coal-mining area? They may have assumed your house is at risk if so.
(Experience of subsidence here.)

In addition to coal mining as a subsidence risk, are you on clay soils or on chalk?

House is about 30 years old, on mixed clay/ loam, not heavy clay. Good-quality farmland before this estate was built. Not a mining area. Not fenland. Not flood plain. I lived a few doors down prior to buying this house and no issues there either.

Gut reaction is either it's a mistake (wrong property), or a pre-emptive move prior to trying to drop price. I said to Estate Agent that buyer is welcome to organise another survey, then came the drip-feed that they want me to pay. Estate agent says the cost is a small amount to pay, given they're paying me a good price (I think it's equally a small amount for them to pay if they want to know this information.)

Estate agent says he'll be back to me with what he has in writing.
I'd spoken to my solicitor this morning, who said he'd answered some questions from buyer's solicitor a fortnight ago - no indication anything like this was in the pipeline. Estate agent must have chased buyer's solicitor today, as Solicitor had asked me to see if they know what's going on, and now this has cropped up.

I've never heard of a subsidence survey. Is this really not crossed wires? The EA just wants to get his commission when you're this far down the line so of course he'll say it's a small amount for you to pay. I'd stand firm and refuse to pay for it.

Thank you to everyone who replied. It helped to know I wasn’t wrong.

Update (for what it's worth): Currently following Solicitor's advice, have told Estate Agent that Buyer may carry out a survey, but it'll be his survey at his expense, not mine, and am now sitting tight to see what happens.

That was 4 days ago... not heard a thing since.