If work is carried out without approval it is classified as unauthorised. The Authority has powers to take legal action to require an application to be submitted and to open up work to check for adequacy. This may result in a fine. You could also be fined for failing to comply and pay to have offending work altered. In extreme cases work may be required to be taken down. Resulting in a criminal conviction.
Probably the most serious problem will be the affect on any future house sale. Approval Notices and Completion Certificates are now needed as standard for any conveyancing and you are more than likely to experience problems selling. You may also find that your house insurance is invalidated.
By telephone: 01628 796870
By email: building.control@rbwm.gov.uk
By post: RBWM Building Control Consultancy, Town Hall, St Ives Road, Maidenhead SL6 1RF