If it's class G airspace and outside the ATZ it's perfectly legal - stupid but legal. At some airfields with ILS you could conceivably find yourself sharing the same bit of airspace with anything up to '747 size (Manston for instance) with the accompanying wake turbulence. Remember ATC at these airfields might not have radar to warn the '747 of your presence, while some might have radar but are unable to use it for some reason.