Hello and thanks for using Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
As the extension was carried out so long ago, you have nothing to worry about as regards ***** ***** taking any enforcement action under planning permission or Building Regulations- Councils can't take enforcement under Building Regs if the work was carried out over 12 months ago, and they can't take any enforcement action under planning permission if the work was done over 4 years ago.
Therefore, the only issue you have to bear in mind is that you are buying the property in its existing condition and your Solicitor will not be able to confirm to you that the extension was carried out in accordance with the then Building Regulations.
Your Solicitor may ask the Seller to pay for what is called a Building Regulations indemnity policy, but this only protects you from any enforcement action taken by the Council and which will satisfy your Mortgage Lender, if indeed you are having a Mortgage. The policy does not, however, protect you against any faulty workmanship carried out at the time. Indemnity policies are normally requested where an extension was carried out without Building Regulations, and where the work was carried out under 15/20 years. Therefore, depending when in the 90's the extension was carried out, your Solicitor may or may not make this request.
In summing up, provided you ar ehappy with the condition of the extension, you have nothing to worry about.
I hope this assists you and sets out the legal position.