Roger....I used an airbrush a lot some years ago ( not on a car though) and its a technique you will need to practice for a while before letting yourself loose on a car panel. I've used Chipex paint on similar sized areas and it is possible to get a decent finish if you build the surface up slightly above the paint work and then when it has hardened off fully, very carefully rub down with 1200 and 2500 grade wet and dry used wet followed by a gentle polishing compound.
Your Connaught Green should have no clear coat and as Dave says, if the colour comes off with an abrasive polish that will give you your answer. Certainly my Sport Green had no clear coat finish. Its strange that my Ink Black Roadster does have a clear coat finish....I have no idea why!
