ACA (Associates): "Any person" after qualifying Chartered Accountancy and getting his name entered in register of members is called as Associates. He / she can use after name as A.C.A. (e.g. i m a ACA, employed)
FCA (Fellows): following "category of members", whose names gets registered as Fellows on "an application made in a prescribed manner" to use FCA after there name- category, 1.Member, "who is an Associate, in continuous practice" for atleast 5 yrs.
2.Member, "who is an Associate for continuous period of not less than 5 yrs AND who possess qualification, experience as prescribed, equivalent to that of continuous practice.
Now in nutshell, a) To be an ACA, NEED NOT be in practice. b) To be FCA you should fufill either of above two category...