A Commencement Notice is required under Article 9 of the Principal Regulations (Building Control 1997) for specified buildings or works; the requirement for this has barely changed since the 1990 Act, other than the requirement for accompanying documentation and registered professionals for certain specified buildings or works.

Failure to comply with any requirement to which section 17(2) of the 1990 Act applies shall be an offence.

For many buildings/works where an FSC and/or DAC is required, the building can’t be occupied without valid certification i.e. granted fire safety certificate, granted disability access certificate.

Failure to lodge a commencement notice and/or to occupy the premises without valid certification under the BCA is an offence.

SI 9 of the 2014 Building Control Regulations ensures that this legislation breach, i.e. non-submission of documentation, cannot be regularised.
The Building Control Authority may enforce the regulations by serving enforcement proceedings for the commencement of buildings/works without notice to the Local Authority in the form of a Commencement Notice (i.e. enforcement for failure to submit), then prosecute this failure in the courts.
According to Section 17 of the Act, prosecution proceedings against defaulters must be instituted within 12 months after the date of discovery of the offence but not later than 5 years after the building/work’s completion date for which the offence is alleged.
The BCA may decide to serve an enforcement notice without proceeding to prosecution, placing the particulars on the statutory register before 12 months expire from their discovery of the offence for the following reasons: financial consideration, proportionality of the offence to its consequences, the common good, and the building/works being certified by the local authority as fully compliant with Building Regulations (if not the administrative requirements of the Building Control Regulations).
If a building has commenced without a Commencement Notice, and this is brought to the attention of the BCA and/or owner, the owner may apply for a Commencement Notice for the remainder of the building/works (similar to building an extra storey on top of an existing building). In this case, the corresponding Completion Certificate would only cover the Commencement Notice works; those conducted already can never be the subject of a Completion Certificate for legislation purposes, but that doesn’t mean they are non-compliant with Building Regulations. This may impede the owner legally speaking but does not concern the BCA.
The owner’s remaining option it to demolish and begin again or face the BCA enforcing, prosecuting, and requesting removal. In this instance, the judge may consider proportionality.

Note

If you are in any doubt as to your situation, contact your local building control authority.

What happens if a development requiring a Commencement Notice commences without one?