Regretfully admitting leader of British airstrike is missing (6)
I believe the answer is:
afraid
'regretfully' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for afraid that I've seen before include "Feeling anxiety or fear" , "Scared, apprehensive" , "Scared - politely regretful" , "with butterflies" , "makes one panicky" .)