Revolutionary force concerning mardy bum (3,4)

I believe the answer is:

red army

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'revolutionary force' is the definition.
'red army' can be an answer for 'force' (I've seen this before). I am not certain of the 'revolutionary' bit.

'concerning mardy bum' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'bum' indicates anagramming the letters (bum can mean faulty or wrong).
'mardy' anagrammed gives 'darmy'.
're'+'darmy'='RED ARMY'

Can you help me to learn more?

(Other definitions for red army that I've seen before include "Soviet troops" , "Left soldiers" , "Revolutionary fighters" , "force" , "Leon's offensive baby" .)

I've seen this clue in The Guardian.

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