Poles in Brussels start to examine result (5)
I believe the answer is:
ensue
'result' is the definition.
('ensue' can be a synonym of 'result')
'poles in brussels start to examine' is the wordplay.
'poles' becomes 'ns' (North and South poles).
'in' is an insertion indicator.
'brussels' becomes 'eu' (Brussels is a metonym for the European Union).
'start to' indicates taking the first letters.
The first letter of 'examine' is 'e'.
'ns' put inside 'eu' is 'ensu'.
'ensu'+'e'='ENSUE'
(Other definitions for ensue that I've seen before include "Occur as a result (of)" , "Come to pass" , "Follow as a consequence" , "Transpire" , "Proceed" .)