The poo really does hit the fan if they do start looking for the aircraft and discover the pilot is already knocking a pint back.
And that happens on a weekly(if not more regular) basis.
Just remember to phone in .....especially if your destination is a bloody farm strip in the middle of nowhere.
I agree that ATCO's should not make it up. MATS part 1 states
1.2 The Manual of Air Traffic Services contains instructions and guidance for controller providing Air Traffic Services to cater for both routine and many emergency situations.
However, nothing in this manual prevents controllers from using their own discretion and initiative in response to unusual circumstances, which may not be covered by the procedures herein.
For me that was always a big enough catch all to allow me(and members of my watch) to have a bit of wiggle room...you may call it making up rules for the benefit of the pilot. I called it concern.