Open plan extension - no planning permission!

[englishnose]

We are in the process of buying our first house, due to exchange in the next week or so.
It’s a mid-terrace with a conservatory (5.6m x 2.4m) which after reading through planning consent laws seems to fall under permitted development. (We’re also sure it’s over 4 years old, trying to find out from the seller currently.)
The issue is that the back wall of the property has been removed so that the conservatory/lounge/kitchen is open plan - I’m pretty sure as this is an alteration to the original structure it would require planning consent?
DH has already emailed the council (this weekend) which I think means we can’t get indemnity insurance?
Any advice would be appreciated on what cost we would incur with retrospective planning, or what could be the worst case scenario?

If you’re in a position to exchange your solicitor should have dealt with all necessary enquiries. They’ll ask plenty without notifying you and the sellers will cover the indemnity insurance. Happened to us with our current home- had no clue until we got the final pieces of paperwork and was told about the policy after completion

Does it have building regs (building control) sign off? Even if it didn't need planning, it would need regs. Most Council's let you search online.

Contacting the Council was unwise (don't think solicitor or vendor will be happy) but it's done now.

Sorry I have no advice but just curious, why was contacting the council unwise?

Thank you for the replies!
I’m guessing by contacting the council, if they were not already aware of any changes to the structure - they now are.
After messaging the seller directly (it’s a Purple Bricks sale) they have informed me the extension was there when a family member bought the property originally, which was over 30 years ago. Would I be unreasonable to ask for some evidence of this in the event we require it further down the road?

Surely this is what you pay solicitors for ?

Nomatchingsocks, how were the issues with your sale resolved? We’re there any costs to you?

Contacting the council is unwise because it means no one can indemnify against the lack of building control sign off as the council has been alerted. The OP's husband has potentially made things very difficult for the seller and possibly scuppered their own purchase. Unless he didn't tell them the property address.

No cost to us at all. The seller paid for the policy and we have never had an issue- fitted regs at the time but these things change. Previous owners also went over a sewer pipe because at that time you owned them if they were in your boundaries- this has since changed and Thames water own them now and if the conservatory was added now we would need an access cover. Regs change all the time BUT your solicitor SHOULD have carried out all of the necessary searches and enquiries and would have dealt with this. We are now selling this property and have had to deal with this (with answering them with our solicitor) and as the seller we are now paying for an indemnity policy (£170) I doubt the buyers are aware of this as we wasn’t the first time round