Building permit

Hoping someone can help me here.
I know of a property for sale that has had an extension, by the way of a room added on the back, but I have heard from a neighbour that a building permit was not obtained for the extension.
What i don't know is whether any of the inspections or documents would show this.
Can anyone shed any light on this please.
Tge Section 32 will show this, look for 'any improvements' If it is not approved and you buy at auction, it is your problem. You could of course go to the council, but that would alert them to this, on the other hand if it has been there for a long time I think the council just accepts it. (don't take that as gospel)