Charles and Mike showing wide difference (5)
I believe the answer is:
chasm
'wide difference' is the definition.
(I've seen this in another clue)
'charles and mike' is the wordplay.
'charles' becomes 'Chas' (shortened form).
'and' is a charade indicator (letters next to each other).
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'chas'+'m'='CHASM'
'showing' acts as a link.
(Other definitions for chasm that I've seen before include "Abyss" , "Pit" , "Deep opening in the ground" , "big break?" , "Deep cleft in ground" .)