AyrTC - a brief look at the second attachment re opening hours. Chap 4.1 states that flights for public transport are prohibited by the ANO.
When I was at PO we never had any difficulty - if a flight was late, probably Loganair returning from Benbecula would be the only one, I or the other ATCO told AFS, then we all stayed until he'd shut down, and claimed overtime.
When ATCOs were being used in the '81 Civil Service strike ( we were still linked to the CS for pay rises ) H&I had been exempted from the ballot and any subsequent action as we were deemed an essential service for the communities.
Mind you the penny-pinching hadn't started then and any out of hours call-out paid a minimum of 3 hours overtime plus mileage at duty rate - hence very popular!