One half of Macclesfield stupidly admit criminal activity (4,5)
I believe the answer is:
come clean
'admit criminal activity' is the definition.
'come clean' can be an answer for 'admit' (I've seen this before). I am not sure about the 'criminal activity' bit.
'one half of macclesfield stupidly' is the wordplay.
'half of' suggests halving the letters.
'stupidly' is an anagram indicator (a stupid ordering of the letters).
'macclesfield' with half the letters taken is 'maccle'.
'one'+'maccle'='onemaccle'
'onemaccle' anagrammed gives 'COME CLEAN'.
Can you help me to learn more?
(Other definitions for come clean that I've seen before include "Admit" , "Make honest admission" , "Reveal dirty secrets" , "Let the cat out of the bag" , "Own up (informal)" .)