In favour of student picketing centre of Exeter for fuel (6)
I believe the answer is:
petrol
'for fuel' is the definition.
(petrol is a kind of fuel)
'in favour of student' is the wordplay.
'in favour' becomes 'petr' (I can't justify this - if you can you should believe this answer much more).
'of' becomes 'o''.
'student' becomes 'l' (as in L-plates for learner drivers).
'petr'+'o'+'l'='PETROL'
'picketing centre of exeter' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for petrol that I've seen before include "Fuel for the internal combustion engine" , "Fuel for road vehicles" , "Common motor fuel" , "The juice" , "Mineral oil refined as fuel" .)