@AC - Entrapment - not perfectly acceptable
I'm not a lawyer, but even a quick google of the subject shows that you're not entirely correct here. Cases have been dismissed in the UK on the grounds that they were entrapment. It sounds as though the case you're highlighting where they actually persuaded the person to commit a crime, the judge should have thrown the case out.
From my brief read on the subject, it appears that police are allowed to create an opportunity for a crime (leave goods unprotected then arrest the thief, or run a shop on the dark web that can be contacted for gun purchase), however they cannot encourage you to commit that crime. So I assume that they could not leave some goods unprotected, then pay someone to go and steal it for them. However it's up to the judge to conclude that was done, you cannot submit it as a defence to the jury.
Once again - not a lawyer, just breaking down the results of a quick search on the subject.