Incentive to take a vehicle round the right circuit (6)
I believe the answer is:
carrot
'incentive' is the definition.
(as in a carrot and stick)
'a vehicle round the right circuit' is the wordplay.
'a vehicle' becomes 'car' (car is a kind of vehicle).
'round' means one lot of letters goes inside another.
'the right' becomes 'rt' (abbreviation as in Rt Hon- the Right Honourable).
'circuit' becomes 'o'.
'rt' placed around 'o' is 'rot'.
'car'+'rot'='CARROT'
'to take' acts as a link.
(Other definitions for carrot that I've seen before include "Pointed vegetable" , "Vegetable to entice the donkey" , "orangey colour" , "Orangey vegetable" , "veg" .)