On site approval

Enforcement appeals

If a local authority believes that your building work contravenes the Building Regulations, they may serve you with an enforcement notice requiring you to alter or remove work which contravenes the regulations. If you believe that your work does comply and wish to appeal against this notice you can:

Advise your local authority that you wish to obtain a written report from a suitably qualified person about the compliance of your work with a view to persuading the authority to withdraw the notice. In this event the 28 day period given by the local authority to rectify the building work is extended to 70 days.
Appeal against the notice in the magistrates' court and demonstrate there that your building work complies. This option can be used either as an alternative to the above, or if proceedings under that option have been unsuccessful. You must make your appeal within 28 days of receiving the notice or within 70 days if you have used above option first.

If you are successful with either option, your local authority may be required to pay your costs.

If on the other hand you believe that your work cannot be expected to comply with one or more of the requirements in the Building Regulations because they are too onerous or inapplicable, you do have the right to apply to your local authority for a relaxation or dispensation of the requirement(s) in question in order for your completed building work to be considered to achieve compliance.

Your application must be made within 28 days of receiving the enforcement notice from your authority. If they refuse your application you have a right of appeal (in England) to the Department for Communities and Local Government or (in Wales) to the Welsh Assembly Government against that refusal, providing you do so within one month of that decision. However, if you take this course of action in response to an enforcement notice, and if you have originally maintained that your work was in compliance, your case is likely to be more difficult to justify.

https://www.planningportal.co.uk/wales/building-control/determinations-and-appeals