Untidy soldiers may eat here (2,1,4)
I believe the answer is:
in a mess
'soldiers may eat here' is the definition.
The definition suggests a singular noun which matches the answer.
'untidy' is the wordplay.
I cannot quite see how this works, but
'untidy' could be 'mess' (I've seen this before) and 'mess' is present in the answer.
The remaining letters 'ina' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for in a mess that I've seen before include "Tucker here for Tommy" , "at sixes and sevens" .)