The local authority has to see that building work complies with the Regulations. If the work does not comply, you may be asked to alter or remove it. If you fail to do this, the local authority may serve a notice requiring you to do so.
If you have already completed work without approval it is possible to gain retrospective approval by making a Regularisation Application. In order to gain approval you will need to provide all the necessary information and where requested destructive investigations may be needed to enable the surveyor to assess whether the building complies.