The actual statute that has force of law in the relevant jurusdiction, i.e. the U.K. where the U.K. police would be acting, is The Diplomatic Privileges Act 1964. (politics.stackexchange.com)
It is an organization of law, primarily built by lawyers, as such the notion of «precedent» is more important than actual statutes themselves. (politics.stackexchange.com)
Try as we might, we weren't able to track down the actual statutes mentioned here. (cattime.com)