Capricious informer divides Morecambe (7)
I believe the answer is:
erratic
'capricious' is the definition.
(I've seen this before)
'informer divides morecambe' is the wordplay.
'informer' becomes 'rat' (synonyms).
'divides' means one lot of letters goes inside another.
'morecambe' becomes 'eric' (I've seen this in other clues).
'rat' going inside 'eric' is 'ERRATIC'.
(Other definitions for erratic that I've seen before include "Volatile" , "on irregular path" , "Irregular in pattern or movement" , "Cartier (anag.)" , "Fluctuating" .)