Shock when nonsense's written about Northern Ireland (8)
I believe the answer is:
astonish
'shock' is the definition.
(I've seen this before)
'when nonsense's written about northern ireland' is the wordplay.
'when' becomes 'as'.
'nonsense' becomes 'tosh' (tosh is a kind of nonsense).
'written about' indicates putting letters inside.
'northern ireland' becomes 'ni'.
'tosh' enclosing 'ni' is 'tonish'.
'as'+'tonish'='ASTONISH'
(Other definitions for astonish that I've seen before include "Dumbfound" , "'knock for six'?" , "Greatly impress" , "Stagger" , "Floor" .)