This is a very old bone of contention and I doubt there is a resolution [even on Pprune]. The danger here is overall erosion of the police service efficiency.
There are some [particularly American police] who believe that a 'civvie' cannot do any police job in the air. Almost as if we were born to be police officers rather than trained and kicked into shape.
It may be rubbish to think that way, we were all born civvies ... but it is debatable whether many police officers really do revert to that state after 30 years of service.... and you can create an efficient observer quite easily even if they might be short of that certain something. The end product can be good subject to such as those 'ifs' pointed out by Tigerfish but there maybe a wider non-aerospace issue here.
For some years there has been a move to civilianise everything in the police service because it is allegedly cheaper. You can probably cut a third off the wage costs on a one-to-one civilianisation. But it does not actually work that way.
Time and time again over the last 30 years there have been instances of getting rid of the Admin sergeant or another police post and civilianising the office... but what happens... within months the replacement cannot cope and 'they' need more office space because there are three of them!
The same with the new semi-civilian CPSO's [the cheap undertrained and poorly resourced replacement police persons] ... they wander around in pairs... if not threes for mutual support .... that is not economical or efficient when compared with their predessors who did the same job solo.
My point is that this theme reads across the whole service and erodes efficiency [and sounds the death knell of the police service as we know it?]. Although they may not be as flexible as they used to be [potentially because the easier pressures upon the civvie staff as a whole read across] real police officers can still contribute greatly to the the requirement for air units to remain 'lean and mean' where [perhaps!] the easier requirements related to some civilian staff tend not to.