contact your local council and ask to see the planning officer,you may have to apply for retrospective planning,but he is the best person to advise you.If your up front and explain the situtation they can be helpfull.
For building regulations if the works were undertaken prior to 1985 then the Council cannot entertain a regularisation certificate application. Where works are undertaken without bg regs approval the choices are to revert the area back to its original state or ensure compliance with the regs in force at the time.
You always have the option to comply with todays regs but the thermal insulation standards are massively improved over pre 1985 regs.
I think the issue is what any prospective purchaser would think, and in particular there mortgage company. Unfortunately I think that you need some specialist legal advice.
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