I don’t believe this is the case, every now and then we see prosecutors using an obsolete unenforced law or an unexpected edge case of some law to come after people.

A great example is the CFAA. It has been judicially narrowed after court battles, because in its original form it was overbroad and criminalized basic, common things. Prosecutors abused it in order to get political wins until they were finally stopped.

This is unfortunately fairly common. Legislators either push for too much or don’t understand how the law might be applied, and innocent people suffer until someone wins a big expensive set of appeals.

Edit: I realize now you may be talking about the UK in particular, in which case you don’t even get this shoddy level of protection as “Parliament is sovereign” (lol).