Barrister and casual worker having endless fun (7)
I believe the answer is:
templar
'barrister' is the definition.
(barrister belonging to the Inner or Middle Temple)
'casual worker having endless fun' is the wordplay.
'casual worker' becomes 'temp' (short-term or temporary worker).
'having' means one lot of letters go next to another.
'endless' means to remove the last letter.
'fun' becomes 'lark' (what a lark).
'lark' with its final letter taken off is 'lar'.
'temp'+'lar'='TEMPLAR'
'and' is the link.
(Other definitions for templar that I've seen before include "Knight of a religious and military order" , "Member of religious and military order" , "barrister" , "Old Crusader Knight" , "Simon - (The Saint)" .)