First person set up police force, getting local six-footer (5)
I believe the answer is:
emmet
'local six-footer' is the definition.
(dialect term for an ant)
'first person set up police force getting' is the wordplay.
'first person' becomes 'me' (first-person pronoun).
'set up' says the letters should be written in reverse (in a down clue, letters go up).
'police force' becomes 'met' (short for Metropolitan Police Service).
'getting' says to put letters next to each other.
'me' written backwards gives 'em'.
'em'+'met'='EMMET'
(Other definitions for emmet that I've seen before include "Robert ...., .... Bergin," , "one holidaying in Cornwall" , "tourist in the South West" , "Cartoonist" , "someone doing the Eden Project?" .)