Involved with police special on gold to help promotion (9)
I believe the answer is:
cosponsor
'involved with police' is the definition.
I can't tell whether this defines the answer.
'special on gold to help promotion' is the wordplay.
'special' becomes 'sp' (abbreviation).
'on' indicates putting letters inside.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'to' says to put letters next to each other (I've seen this in other clues).
'help promotion' becomes 'coons' (I can't justify this - if you can you should give a lot more credence to this answer).
'or' after 'coons' is 'coonsor'.
'sp' inserted inside 'coonsor' is 'COSPONSOR'.
Can you help me to learn more?
(Another definition for cosponsor that I've seen is " Jointly finance".)