You should check the ANO, section 2 page 5 and 6 or post the question in the military forum.
After the airport operational hours, at Biggin Hill anyway, ATC have no involvement of what goes on, what those aircraft which may be exempt from the low flying rule do in Glass G airspace is their business .
At the end of the day, outside the operational times published in the AIP when the airport is closed, the ATZ is in-active so, providing aircraft obey the relevant rules of the air then that’s up to them. It would be different if the airport were in CAS or (or a Government AD) or were listed as active H24.
Of course if low flying or landings/takeoffs are really taking place out of hours (which I doubt they are) then let’s hope nobody attempts it on the 26th April!
http://www.bigginhillairport.com/ANT_pr1.pdf