Snaith Days by Keith S Ford (superb book if you can find it) has the following on pages 45-46:
Base and aircraft were allocated operational call signs for both R/T (voice) and C/W (morse) communications which were changed daily (June 1943): e,g. aircraft was 'Graceless, base was 'Agnola'. Aircraft of 51 squadron were designated mostly MH but some LK: e.g MH-A, LK-D. Apparently MH aircraft had different call signs to LK aircraft.
Near the end of the war some call signs were used for a longer period.
The phonetic alphabet is listed: Able, Baker, Charlie, Dog, Easy, Fox, George, How, Item, Jig or Johnny, King, Love, Mike, Nan, Oboe, Peter, Queen, Roger, Sugar, Tara, Uncle, Victor, William, X-Ray, Yoke, Zebra.
An example for 1944 landing at Snaith is given. The aircraft is MH-D with 75 minutes endurance being stacked and given a height to fly at:
A/c: 'Hello Agnola, this is Graceless D Dog 75, Over'
Flying Control: 'Hello Graceless D Dog, Agnola answering, height to fly 1,500, QFE 1,000 Over'. (QFE 1,000 meant set your altimeter to airfield barometric pressure of 1,000 millibars so that it would indicate zero altitude on landing).
The a/c would acknowledge by repeating height to fly, and join the circuit at 1,500 ft, having listened for the broadcast of the a/c ahead of it to ascertain its code letter and call sign so that the pilot could keep a check on its position whilst in circuit and when landing.
When an a/c had landed the next higher circuit would be called into land:
Flying Control: 'Hello Graceless D Dog, this is Agnola, prepare to land. Over'.
As D Dog continued its landing it would call at the various times 'Flaps', 'Wheels' and finally 'Funnels' just before final approach. This was to keep other a/c informed. After 'Funnels', if the runway was clear, Flying Control would say 'Pancake' (if the pilot couldn't land for some reason he would call 'Overshoot' and rejoin the circuit. Once landed and after clearing the runway he would call 'End Clear'.