Incompatible peacekeepers set to tour part of UK (11)
I believe the answer is:
uncongenial
'incompatible' is the definition.
('uncongenial' can be a synonym of 'incompatible')
'peacekeepers set to tour part of uk' is the wordplay.
'peacekeepers' becomes 'un'.
'set' becomes 'congeal' ('congeal' can be a synonym of 'set'**).
'to tour' is an insertion indicator (to tour can mean to go around).
'part of uk' becomes 'ni' (Northern Ireland).
'congeal' placed around 'ni' is 'congenial'.
'un'+'congenial'='UNCONGENIAL'
(Other definitions for uncongenial that I've seen before include "Disagreeable" , "Not friendly or pleasant" .)