If a scenario like this was to happen again next week, how would your changes stop it from happening?
What's stopping the police from saying X was the informer when it was Y?
DPP will have no way of knowing...
If DPP is lied to then its Perjury. Then it goes down the chain. Who knew about it etc. Then charged with the new criminal offence of breaching legal privilege. Coppers and Lawyer both charged.
Legislation cannot stop criminal behaviour. No amount of legislation can stop what happened from happening again. It can only make more people more accountable and bigger punishment if caught.