A valid commencement does not have an expiry date once commenced within the 14-28 day period and substantial works have been carried out; a new Commencement Notice is not required after a prolonged delay.
However, to comply with Buildings Regulations requirements, it’s recommended that the builder conduct due diligence and the Building Control Authority issue an S11 request to show Building Regulations compliance.
Typical S11 Request
Note: if you are in any doubt, contact your local Building Control Authority.