... but there are plenty of M reg aeroplanes doing dodgy charters.
....
...the problem is so overwhelming.
A pretty bold statement. If you actually KNOW that to be a fact, then why do you not tip off the authorities? If I was a legitimate charter operator, I certainly would.
I would suspect that it is actually
less likely that IOM aircraft are used for dodgy charters due to the fact that everyone knows that the IOM register does not cater for CAT. I don't doubt it happens though, but I'm sure it's not as prevalent as you suggest, and I'm certain that the problem is not of an "overwhelming" nature.
And another thing; Why special branch - what do they have to do with it?