We are about to embark on a house extension that would increase our home from a 4 bed to 5. We are financing by paying for the “shell” of the extension with cash then hoping to remortgage (current deal up in November) to finish off the job and recoup some of our cash in bank savings. Does anyone know how we “officially” change the house from a 4 bed to 5 for mortgaging purposes, which authority this with and if we need to? We don’t want the mortgage company to do a driveby valuation and not know we have increased the footprint/bedrooms/spec of the house.