Minister with opportunity backed Tube (10)
I believe the answer is:
chancellor
'minister' is the definition.
(type of government minister)
'with opportunity backed tube' is the wordplay.
'with' says to put letters next to each other.
'opportunity' becomes 'chance' (synonyms).
'backed tube' becomes 'llor' (I can't explain this - if you can you should give a lot more credence to this answer).
'chance'+'llor' is 'CHANCELLOR'.
Can you help me to learn more?
(Other definitions for chancellor that I've seen before include "chief minister" , "Head of government" , "Titular university head" , "See 8" , "11 17 down [CABINET MINISTER]" .)