The CAA are urging the public to do their job because they're unable to do it themselves. I was pretty much told this recently by a senior member of flight safety team.
Because the burden of proof is that of a criminal court they just don't have the powers, manpower and budget (and let's face it skills).
It's much better to hassle the people they know are trying to do a good job, but might have forgot to pack their Pooleys rather than get involved with the "private" flights going on in the background.