Father pocketing English group's old Spanish money (6)
I believe the answer is:
peseta
'old spanish money' is the definition.
(I've seen this before)
'father pocketing english group's' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'pocketing' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'group' becomes 'set' (both can mean a collection).
'e'+'set'='eset'
'pa' enclosing 'eset' is 'PESETA'.
(Other definitions for peseta that I've seen before include "Spanish bread once" , "Obsolete coin" , "little cash is required" , "Spanish coinage" , "Spain's former currency unit" .)