Having spent 16 years as a Shanwick Clearance Delivery Officer CDO prior to my present job we would always advise on passing the clearance of any change...i.e.
Bigjet123 be advised your requested flight level is not available, Shanwick clears Bigjet 123 to destination KJFK via track Alpha maintain FL360 Mach .080 from 57N 10W FL370 is not available........its 17 years since I did that job but thats how we did it then at a time that the Clearance Delivery frequency was one of the busiest frequencys in Europe
