Not quite Mr zippo,
I think you missed the fact that we have been in there on non-air ambulance flights with fee paying pax, no justification required, just get permission, pay the fees and follow the rules. I think the point that clears it up is that 'private' flights will not be accepted but public transport flights in piston twins will be (if you can get a slot!)
As for ambulance flights I always found them very accommodating, even during peak hours they would somehow find a way to squeeze us in.....fantastic. Used to get the spotters all excited as I recall; at one point an ops landrover came hurtling out '4-up' trying to find out where 'Papa-Zulu' was, poor spotters didn't realize we'd changed aircraft before departure due to a technical problem and thought they'd missed PZ on her inaugural EGLL flight!!
PP