No. 1 detectives upset having to accept rubbish, overbearing command (9)
I believe the answer is:
dictation
'overbearing command' is the definition.
'dictation' can be an answer for 'command' (synonyms). I am not sure about the 'overbearing' bit.
'no 1 detectives upset having to accept rubbish' is the wordplay.
'no t' becomes 'no i' (resembles No t).
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'upset' says the letters should be written in reverse.
'having to accept' is an insertion indicator.
'rubbish' becomes 'tat' (tat can mean rubbish or poor-quality material).
'noi'+'cid'='noicid'
'noicid' backwards is 'dicion'.
'dicion' placed around 'tat' is 'DICTATION'.
Can you help me to learn more?
(Other definitions for dictation that I've seen before include "office activity" , "Speech for transcribing" , "Speaking of words to be taken down" .)