He questioned large Northumbrian maybe storing resin used by fuel firm (6,9)

'he questioned' is the definition.
(British quiz show host)

'large northumbrian maybe storing resin used by fuel firm' is the wordplay.
'large' becomes 'big' (synonyms).
'northumbrian maybe' becomes 'NE' (Northumbria is in the North East of England).
'storing' means one lot of letters goes inside another.
'resin' becomes 'amber' (amber is a type of resin).
'used by fuel firm' becomes 'gasco' (I can't justify this - if you can you should believe this answer much more).
'big'+'ne'='bigne'
'amber'+'gasco'='ambergasco'
'bigne' going around 'ambergasco' is 'BAMBER GASCOIGNE'.