Most police checks occur before a person is employed by a company but in some cases, an employer may ask an existing employee to provide one. The first question that usually comes to mind is "Why am I being asked for a police certificate?" It's a good question and it’s important to understand the company's point of view and why it’s asking for a police check to be conducted.
https://www.finextra.com/blogposting/21245/why-employers-ask-for-police-certificates