I was trained by PPL instructors in the UK. Some were excellent, some were rubbish, just like those with CPLs. Many would have been CPLs if they hadn't been prevented from holding the CPL due to not being able to have a Class One usually because of eyesight (one CFI had glasses like the proverbial bottom of a coke bottle !)
The difference between the case here in Aus, and that in the UK, is that it really isn't that difficult or expensive to upgrade a PPL to a CPL here, but in the UK it really was a mammouth and unbelievably expensive exercise, including such delights as eight month waiting lists for commercial flight test, plus prior to the introduction of the BCPL in 1989 you had to have 700 hours to hold any kind of CPL over there.
The other difference is that in the UK most schools operate as clubs, mainly becuse it is easier to survive that way (where I was, the bar and pool table was the only part of the club that made much money and subsidised all the flying that didn't happen when it was raining) Here in Aus most flying training organisations are run by private companies; that way you don't get lose cannons on the committe wrecking people's livlihood!
So, IMHO here in Aus all instructors should hold a CPL, especially if the knowledge and hours requirements are the same. IF they are good enough to instruct, then they should be able to upgrade to CPL without too much effort. If not, you have to wonder what their motivations are.
But PPLs teaching...I shudder at what it would do to the livlihoods of career instructors, and the internal politics if you had PPLs working for nothing along CPLs who worked for next to nothing; there would always be an unhealthy rivalry.
This was discussed on the AOPA website before they closed it to non-members. Could well be all this nonsense is their idea, not CASA; why on earth can't they stop meddling? Let them do thier AUF thing, and leave us professionals to get on with our work.
Have a nice day.