Capital Radio still ultimately trailing tour and single (7)
I believe the answer is:
tripoli
'capital' is the definition.
(capital of Libya)
'radio still ultimately trailing tour and single' is the wordplay.
'ultimately' says to take the final letters.
'trailing' says to put letters next to each other.
'tour' becomes 'trip' (I've seen this in other clues).
'and' says to put letters next to each other.
'single' becomes 'I' (one).
The last letters of 'radio still' are 'ol'.
'ol' after 'trip' is 'tripol'.
'tripol'+'i'='TRIPOLI'
(Other definitions for tripoli that I've seen before include "Place in Libya" , "city on the Mediterranean" , "where there's been regime change" , "Libyan port" , "North African city" .)