Close relative touring part of UK is ominous (8)
I believe the answer is:
sinister
'ominous' is the definition.
('sinister' can be a synonym of 'ominous')
'close relative touring part of uk' is the wordplay.
'close relative' becomes 'sister' (I've seen this before).
'touring' indicates putting letters inside (touring can mean going round).
'part of uk' becomes 'ni' (Northern Ireland).
'sister' going around 'ni' is 'SINISTER'.
'is' is the link.
(Other definitions for sinister that I've seen before include "Suggestive of evil, being lefthanded" , "Forbidding" , "Menacing" , "Suggesting or threatening evil or danger" , "What is left on bearings" .)