Swindle involving current 50p, say (4)
I believe the answer is:
coin
'50p say' is the definition.
(fifty pence is a type of coin)
'swindle involving current' is the wordplay.
'swindle' becomes 'con' (con is a kind of swindle).
'involving' indicates putting letters inside.
'current' becomes 'i' (symbol for electric current).
'con' going around 'i' is 'COIN'.
(Other definitions for coin that I've seen before include "Metal currency" , "Penny, say?" , "Invent a word or phrase - for money?" , "Fabricate" , "Money; devise (a word)" .)