Ha-Ha. Good luck, this happens all the time to Classic RR owners. Atlantic British has a tech tip about this basically saying when this happens time to buy a new ignition switch ($$$) but usually we just keep working the key until it turns and starts.
At one point, we were at a gas station (busy of course) shut off truck, filled tank (painful $40) pay, go to leave, car won't start because key won't turn!!
Cars are waiting to come in a gas up, we can't leave. Very embarassing, shot the key switch full of WD-40 and after like 45min (not kidding) it started and we left. Almost had to get it towed.
One thing to do to avoid this is MAKE SURE not to jar the steering wheel after you shut the car off and pull out the key. If the steering wheel locks than stuck keys are way more likely to result.
Good luck--still on original ignition after 190k. Of course, that's better than our 4.0 which needed a 100 mile tow to Land Rover because it was immobilized. ($$$)
Dan, Local auto electric shop, who does keys and such said not to use the graphite power either, as that little blast of air gets the graphite all the way to the back of the tumbler, and onto the contact block, and being a great conductor, the graphite can short out the switch, engage the starter, etc. He used a non conductive spray grease, might have been the lithium one.