One visiting cathedral: Foreign Secretary perhaps (8)
I believe the answer is:
minister
'foreign secretary perhaps' is the definition.
'one visiting cathedral' is the wordplay.
'one' becomes 'i' (Roman numeral).
'visiting' indicates putting letters inside.
'cathedral' becomes 'minster' (minster is a kind of cathedral).
'i' inserted within 'minster' is 'MINISTER'.
(Other definitions for minister that I've seen before include "Tend" , "Form of address" , "Member of the clergy or of the Front Bench" , "Holder of office in government or church" , "Parson" .)