Gabriel could change into a Labor turncoat (9)
I believe the answer is:
archangel
'gabriel' is the definition.
(I've seen this before)
'change into a labor turncoat' is the wordplay.
'into' indicates putting letters inside.
'labor turncoat' becomes 'rl' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'rl'='arl'
'change' going within 'arl' is 'ARCHANGEL'.
'could' is the link.
Can you help me to learn more?
(Other definitions for archangel that I've seen before include "one coming from above with message maybe" , "Most important of divine messengers" , "Highest ranking member of the celestial hierarchy" , "celestial flier" , "What we call a port" .)