Hi suzy, consult the Solicitor who did the purchase,because on the pre-contract agreement there is a section about disputes and different other things,so I would think if the council were in touch with previous owners,they have not revealed this information and they will probably be liable for the cost,just a quick call will put your mind at rest,but if you don't want the hassle ask the planning officer to come round for a chat,but be very polite to him/her, retrospective permission might well be granted, good luck, Ray