If you use CCTV in a work setting, or other video surveillance, you need to look at the newly updated ICO video surveillance guidance issued this week at https://ico.org.uk/for-organisations/guide-to-data-protection/key-dp-themes/guidance-on-video-surveillance/
The guidance includes law enforcement, but it has been developed to help organisations in the public and private sector, who use video surveillance systems to collect and process personal data. It will help those organisations to stay within the legal requirements of the UK General Data Protection Regulation (UK GDPR) and the Data Protection Act 2018 (DPA 2018).
Amongst the guidance, I find their checklist https://ico.org.uk/for-organisations/guide-to-data-protection/key-dp-themes/guidance-on-video-surveillance/checklist-for-limited-cctv-systems/ particularly helpful, as you can use it as a helpful prompt.