Very distinctive versifier leading a saboteur into small room (5,2,1,4)
I believe the answer is:
clear as a bell
'very distinctive' is the definition.
'versifier leading a saboteur into small room' is the wordplay.
'versifier' becomes 'lear' (Edward Lear).
'leading' is a charade indicator (letters next to each other).
'saboteur' becomes 'sab' (short for saboteur in hunting terminology).
'into' means one lot of letters goes inside another.
'small room' becomes 'cell' (I've seen this before).
'lear'+'a'+'sab'='learasab'
'learasab' placed within 'cell' is 'CLEAR AS A BELL'.
(Other definitions for clear as a bell that I've seen before include "Heard very distinctly" , "Distinct and pure in tone" .)