Currency smuggled into Chelsea, say (5)
I believe the answer is:
franc
'currency' is the definition.
(I've seen this before)
'smuggled into chelsea say' is the wordplay.
'smuggled' becomes 'ran' (I've seen this in other clues).
'into' indicates putting letters inside.
'chelsea say' becomes 'FC' (short for football club - Chelsea FC is an example).
'ran' put within 'fc' is 'FRANC'.
(Other definitions for franc that I've seen before include "One hundred centimes in Benin" , "Swiss currency unit" , "money abroad" , "I'm accepted in Basle" , "It's ready" .)