Thank you very much. This has been great, useful advice. I hope you don't mind a few follow up questions relating to this.
1. As the additional room does not have windows, I believe it is not deemed as 'habitable' therefore (when put up for sale) will be advertised as a studio flat rather than a one bedroom. Will the buyers solicitor definitely ask for Building Regs for the work done even though it is still classed as a studio flat?
2. If it is a requirement before the sale is completed, should one obtain the Building Regulations indemnity policy before request is made from buyers solicitor?
3. Do I have an obligation to tell my solicitor about the change i.e. does it need to be declared?
4. Freeholders consent - how would I know if this should have been obtained?