Old driver is a riot travelling in comfort (10)
I believe the answer is:
charioteer
'old driver' is the definition.
'riot travelling in comfort' is the wordplay.
'riot travelling' becomes 'ariot' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'comfort' becomes 'cheer' (cheer can mean to comfort or gladden someone).
'ariot' put into 'cheer' is 'CHARIOTEER'.
'is a' is the link.
Can you help me to learn more?
(Other definitions for charioteer that I've seen before include "Driver of horse-drawn fighting vehicle" , "Hippodrome racer" , "Driver common in early warfare" , "Driver of Roman vehicle" , "Old carriage driver" .)