Intelligence gatherer dismisses posh British national (4)
I believe the answer is:
scot
'british national' is the definition.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for scot that I've seen before include "Payment" , "---- free: originally free from penalties of taxation" , "Highlander, say" , "Northerner; old tax" , "Burns for one" .)