Blunder, as one may in Balmoral? (3,4,4,2,2)
I believe the answer is:
put ones foot in it
I believe this is a double definition.
'blunder' is the first definition.
(I've seen this before)
'as one may in balmoral?' is the second definition.
(a Balmoral is a type of shoe)
(Other definitions for put ones foot in it that I've seen before include "Commit a faux pas?" , "Bungle" , "usual way to use a sock" , "as one might with one's trainer" , "Make a tactless blunder (3,4,4,2,2)" .)