From the ICO website on exemptions:
"Law enforcement – the processing of personal data by competent authorities for law enforcement purposes is outside the GDPR’s scope (e.g. the Police investigating a crime). Instead, this type of processing is subject to the rules in Part 3 of the DPA 2018. See our Guide to Law Enforcement Processing for further information."
If your bored or just like parsing legal documents, have a look at Part 3.