I am looking at purchasing a second hand semi detached 5 bed property. The property when constructed was extended to include an extra 2 bedrooms up stairs to make 5 and a small bedroom/kitchen/lounge, underneath the 2 extra bedrooms. Planning permission was obtained for the extension, but the door connecting the downstairs part of the extension to the rest of the house was closed off and a separate power/gas supply for it was obtained to make it a seperate self contained granny flat. I have found out through a little investigating that planning permision was not obtained for turning this into a seperate granny flat. I am interested in the property, and keen to return it back to the way the extension was constructed initially. Where do i stand legally in purchasing this property with an extension which is not being used as per the original design?