Sorry, Hoist-T-C, but it's a CAA definition and individual Police Forces have had no real say in it. I agree with your view, of course they are crew but it's the way it is for historical reasons i.e. when policemen were first flown on an experimental basis they were pax and that's the way the rules were written. No one knew if Air Support was the way to go in those days so it was all done as an experiment with hired-in aircraft and pilots on a trial basis. Each Police Force seems to have wanted to make their own minds up so there remains no common policy or strategy although things are improving.
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May the Force be with you - and may Gravity treat you gently..