Senior officer’s broadcast on head of clan and escort (3,5,7)
I believe the answer is:
air chief marshal
'senior officer's' is the definition.
(I've seen this before)
'broadcast on head of clan and escort' is the wordplay.
I cannot quite see how this works, but
'broadcast' could be 'air' (to air on TV) and 'air' is found within the answer.
'head' could be 'chief' (synonyms) and 'chief' is found within the answer.
The remaining letters 'marshal' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Another definition for air chief marshal that I've seen is " Senior officer".)