If a shop has CCTV system installed on its business premises, must it inform the customers of the surveillance? Must it tell customers about the purposes of surveillance?

Generally, it would suffice to put up a notice at the entrance, the reception desk, or at an eye-catching spot on the institution's premises saying, “for security reasons/to ensure service quality, the vicinity of this institution is installed with video surveillance systems”. The institution will be well advised to have a copy of personal data collection statement handy for customer review.