UK sailor turning up in foreign capital (4)
I believe the answer is:
baku
'foreign capital' is the definition.
(capital of Azerbaijan)
'uk sailor turning up' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'turning up' shows that the letters should be reversed in order.
'uk'+'ab'='ukab'
'ukab' back-to-front is 'BAKU'.
'in' is the link.
(Other definitions for baku that I've seen before include "Azerbaijan's capital" , "Capital city of Azerbaijan" , "Caspian Sea port" , "Capital of Azerbaijan on shore of Caspian Sea" .)