Mine conceals Brussels connection (5)
I believe the answer is:
tieup
'connection' is the definition.
I know nothing about this answer so I can't tell whether this works.
'mine conceals brussels' is the wordplay.
'mine' becomes 'tip' (I am not sure about this - if you are sure you should believe this answer much more).
'conceals' means one lot of letters goes inside another.
'brussels' becomes 'EU' (European Parliament is based in Brussels).
'tip' placed around 'eu' is 'TIEUP'.
Can you help me to learn more?
(Other definitions for tieup that I've seen before include "Connection with" , "Business association" .)