Circumvent with the aid of a permit (6)
I believe the answer is:
bypass
'circumvent' is the definition.
(I've seen this before)
'aid of a permit' is the wordplay.
'aid of' becomes 'by' (I can't justify this - if you can you should give a lot more credence to this answer).
'a permit' becomes 'pass' (pass is a kind of permit).
'by'+'pass'='BYPASS'
'with the' acts as a link.
Can you help me to learn more?
(Other definitions for bypass that I've seen before include "Road built to avoid a congested area" , "Road built to avoid another" , "What avoids Newbury" , "Circuitous route (for traffic, fluids etc)" , "Go around" .)