Buy particular joint and be sacked (3,3,4)
I believe the answer is:
get the chop
'be sacked' is the definition.
(I've seen this before)
'buy particular joint' is the wordplay.
'buy' becomes 'get' (both can mean to purchase or obtain).
'particular' becomes 'the' (referring to a particular example of something).
'joint' becomes 'chop' (joint of meat).
'get'+'the'+'chop'='GET THE CHOP'
'and' is the link.
(Other definitions for get the chop that I've seen before include "Be fired (informal)" , "what the butcher might do" , "Secure one for grilling" , "Be sacked" , "Collect one's P45" .)