Don't allow a bachelor to go to the North Pole (3)
I believe the answer is:
ban
'don't allow' is the definition.
(I've seen this in another clue)
'a bachelor to go to the north pole' is the wordplay.
'bachelor' becomes 'B' (abbreviation e.g. BA=Bachelor of Arts).
'to go to the north' shows that the letters should be reversed in order (I've seen 'going to the north' mean this (in a down clue, letters go up)).
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'a'+'b'='ab'
'ab' reversed gives 'ba'.
'ba'+'n'='BAN'
(Other definitions for ban that I've seen before include "'Forbid, prohibit (3)'" , "Officially prohibit" , "outlaw" , "Veto" , "Embargo" .)