Vacant kasbah toured by British spies and worshippers (5)
I believe the answer is:
sikhs
'worshippers' is the definition.
(believers in Sikhism)
'vacant kasbah toured by british spies' is the wordplay.
'vacant' says to hollow out the word (remove centre letters) (a vacant or emptied out form of the word).
'toured by' indicates putting letters inside (tour can mean to go around).
'british spies' becomes 'SIS' (Secret Intelligence Service).
'kasbah' with its centre taken out is 'kh'.
'kh' inserted within 'sis' is 'SIKHS'.
'and' acts as a link.
(Other definitions for sikhs that I've seen before include "certain believers" , "Members of a religion who wear turbans" , "Followers of an Indian religion" , "Adherents of a Punjab religion" , "Believers in religion founded in Punjab" .)