Cranks lose heart but unite in defence (5,5)
I believe the answer is:
close ranks
'unite in defence' is the definition.
'close ranks' can be an answer for 'unite' (I've seen this before). I am unsure of the 'in defence' bit.
'cranks lose heart' is the wordplay.
'heart' is an insertion indicator.
'cranks' placed around 'lose' is 'CLOSE RANKS'.
'but' is the link.
Can you help me to learn more?
(Other definitions for close ranks that I've seen before include "Unite in order to defend common interests" , "to put taxi firms out of business?" , "Display solidarity" , "make cabbies go out of business?" , "Unite as a defensive measure" .)