Interesting thought about Sky Marshals. All ex-military aircrew now working for airlines will have received sufficient weapon training to make them reasonably competent with either the 9mm SLP or the Beretta. Perhaps the Home Office should be approached to pass enabling legislation allowing those with such training to receive approved refresher firearms training should the need ever arise.
We're not talking about Desert Eagle 0.50s on the hip here; just a corps of reasonably competent firearms trained folk available in emergency.
Perish the day when you have to carry a weapon in your flight bag though.