Son held in prison that is importing North American petrol (8)
I believe the answer is:
gasoline
'american petrol' is the definition.
(I've seen this before)
'son held in prison that is importing north' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'held in' means one lot of letters goes inside another.
'prison' becomes 'gaol' (I've seen this before).
'that is importing north' becomes 'ine' (I am not sure about this - if you are sure you should believe this answer much more).
's' inserted inside 'gaol' is 'gasol'.
'gasol'+'ine'='GASOLINE'
Can you help me to learn more?
(Other definitions for gasoline that I've seen before include "American petrol in full" , "Fossil fuel" , "N American petrol" , "US fuel" , "Sole gain (anag.); petrol" .)