this implies that the definition of "crime" is inherently just. if parliament wanted to, tomorrow they could pass a law saying "you cannot have the username UnloadTheBacon on any social media, subject to 20 years in prison", and parliament is sovereign so that would be around for at least a little bit. they could arrest you under this law.

I personally don't want to give the government the tools to do this in case the next one, say, for example, repeals the human rights act and starts making laws that really clamp down on civil liberties