Alarm about Northern Ireland tax (6)
I believe the answer is:
tocsin
'alarm' is the definition.
(tocsin is a kind of alarm)
'about northern ireland tax' is the wordplay.
'about' says the letters should be written in reverse.
'northern ireland' becomes 'ni'.
'tax' becomes 'scot' (I've seen this before).
'ni'+'scot'='niscot'
'niscot' back-to-front is 'TOCSIN'.
(Other definitions for tocsin that I've seen before include "alarm call" , "The sound of an alarm bell" , "Alarm bell to be found in Scot" , "One sounds an alarm" , "An alarm bell or signal" .)