Our internal layout doesn't match the planning consent - Help!

[FlintAndTinder]

We are selling our flat and I have realised that the architect we bought it from submitted her original plans to the council for planning consent, consent was granted, and she completed the internal layout entirely differently. The floorplans at the time we bought it and a layout design board that she left at the property in 2010 show it as it is today. I have photographs taken at a viewing in 2010 before we completed our purchase which illustrate this. We didn't find out until a few years afterwards that the interiors didn't match the one on the council's records, but we did find out - I submitted a half-arsed planning application for something else which I later decided against and withdrew, and I found the old plans but I didn't think anything more than "oh, that's interesting".

We will have lived here for more than 5 years at the time the sale goes through - if it goes through. Obviously this will throw up some concerns to the buyer.

What can we do?

Is there insurance we or the buyers can take out (which we would pay for) against any possible comeback from the council?

Is any comeback even likely given that we have been here for more than 4 years (I'm hazy on the details but I think I saw somewhere that if the council haven't served you a Stop Notice within 4 years of the event, then your current arrangement can continue and becomes approved by default).
Is there an affidavit of some sort we can swear to say we haven't changed anything and we have lived in it all this time?

Was the build signed off?

They may not have been the final plans. Indemnity insurance may be available but not if you find out from the council it is an issue. Can you ask your solicitor to advise. Did it have freeholder's consent?

The seller declared that the works had been completed and there were no outstanding building control or planning issues to be resolved in the Property Information Form. I have that, signed and dated.

I don't think I have a buildings regs completion certificate though. I haven't seen it anyway. The council haven't exactly said it was an issue, but one of the comments on my half-arsed application before I withdrew it was basically "oh yeah, and the plans don't match, that needs to be addressed."

After I posted in despair earlier, I've vaguely recalled a conversation with someone - either council planner or someone else at the council - who said we should have submitted the plans with the old layout as "existing" and the new layout as "proposed", even if that isn't exactly the case, and we may have to change some walls around if the council didn't like it. But I have only the vaguest memory and no records of that conversation. But we haven't had a Stop Notice served or anything, and they've basically been made aware of this issue for almost 3 years now and nothing.

I have asked solicitor to advise. I sort of think it might be a problem but it hasn't actually been one - so I'm hoping there's an indemnity policy I can take.

I have no idea about freeholder's consent - it was a new build and the developer sold it off-plan to the architect (who did ours up as a project) but developed the rest of the flats to a fairly standard finish and layout. The freehold has since been sold on to the other tenants of the building.

Internal layouts aren't normally a planning matter so long as windows and doors are correct as technically it doesn't affect anyone else, so long as it's been built to proper regulations etc it won't matter about the internals. There are a few exceptions such as if you had made it into two properties but I'm guessing that's not the case here!

No, it's still one dwelling.

Thanks to everyone who replied to me. I was panicking something awful because I couldn't find a building regs completion certificate in my file from the purchase, but it turns out that it the internal work was all signed off by NHBC instead so that fulfilled the requirements. What I had needed to do for the sake of planning was just to submit the older drawings or explain the changes, just to link up the two.

Whew!