Stop going on, as one may if boot's too big? (3,1,4,2,2)
I believe the answer is:
put a sock in it
'stop going on' is the definition.
(both can be used to tell someone to stop talking)
'one may if boot's too big?' is the wordplay.
I cannot quite see how this works, but
'one' could be 'i' (roman numeral) and 'i' is located in the answer.
'too' could be 'so' (synonyms) and 'so' is located in the answer.
This may be the basis of clue (or it may be nonsense).
'as' is the link.
(Other definitions for put a sock in it that I've seen before include "Quiten down" , "Shut up! Stuff with footwear?" , "If your shoe is too big, you" , "Stop endless yacking" , "Stop talking (3,1,4,2,2)" .)