ACOP is an abbreviation of Approved Code of Practice. The Health and Safety Commission issue ACOPs to businesses to ensure people understand their statutory requirements. Failure to comply with the requirements of an ACOP will be taken as proof of negligence in a criminal proceeding.
In the UK, building owners are required to ensure that ductwork (ventilation) systems are clean and comply with health and safety regulation.
HML recommend that you clean and organise proper maintenance of ventilation systems to ensure a healthy environment and compliance with ACOPs.
Related: Restaurant Ductwork Cleaning | Risk Assessment