I think in this case, the PO conducting its own prosecutions was simply the continuation of an historic situation. Before the CPS was founded in 1986, each police force had its own prosecutions unit, for example in London, the Met Police Solicitor's. Certain other government departments and bodies used to have their own units and some still do, I think this applies to HMRC, Customs & Excise and latterly the SFO.
None of that excuses for one moment the egregious abuse of power the PO have clearly exercised, nor the largardly manner in which they have compensated those they abused.
So yes, signed and shared!