Soldier eats a dirty biscuit (9)
I believe the answer is:
garibaldi
'biscuit' is the definition.
(I've seen this before)
'soldier eats a dirty' is the wordplay.
'soldier' becomes 'gi' (government issue or general issue).
'eats' is an insertion indicator.
'dirty' becomes 'ribald' ('ribald' can be similar in meaning to 'dirty'**).
'a'+'ribald'='aribald'
'gi' enclosing 'aribald' is 'GARIBALDI'.
(Other definitions for garibaldi that I've seen before include "Italian leader; biscuit" , "Famous Italian" , "hero in Italy" , "Italian nationalist; biscuit" , "Blouse; biscuit; Italian patriot" .)