Ignoring the CIA, FBI and MI5 for now, because quite honestly I can't be bothered with fantasy....Assuming you have found one Policeman and turned him, then he has got himself stationed at am airport, what do you then suggest you do.....like I said earlier, do you remove all the articals he carries, although he is quite entitled too? Picture the scene...
A serious disturbance, airside terminal 1 at Heathrow...Police screech to a halt at a BAA control post...run to the metal detector....
BAA Guard "Got anything sharpe or could be used as a weapon mate?"
Police officer places handcuffs, cs gas, baton on table
BAA Guard, "ohhh you can't take them through here mate, you know the rules, I'll have to call the police"
Policeman "Er what do you think this is a bus conductors outfit?"
BAA Guard "Rules is rules mate"
Police then called, and the whole issue is repeated, meaning more police are called.....
Meanwhile, the fight has now developed and one of the paries is laying in a pool of blood...Ambulance screeches to a halt....crew leap out through metal detector....Well sure you can work out the rest!
After an hour the 22,000 members of the Met Police are all assembled at a BAA control Post, the airport is littered with Police cars...someone mutters..."I hope they don't set fire to anything"
Now you can either do one of 2 things. First, sorry if this is a dull repeat...but you can concentrate on what is more lightly to happen, and sadly that includes airline staff bringing things they shouldn't to work (and in some cases would render them liable to arrest whereever they were)
or
B. put up with the inconvience and at least be reassured that there is less chance of the flight deck door caving in and a grinning man with a sun tan muttering sweet nothings in your ear.
of course if you do option B, then at least if it happens on the ground there will be police who can turn up, with equiptment to try to deal with the problem...they wont all be at a BAA control post waiting in a vicious circle.