Old US president protected by British motorcyclist (5)
I believe the answer is:
biker
'motorcyclist' is the definition.
(I've seen this before)
'old us president protected by british' is the wordplay.
'old us president' becomes 'Ike' (nickname of President Dwight Eisenhower).
'protected by' means one lot of letters goes inside another.
'british' becomes 'br'.
'ike' put into 'br' is 'BIKER'.
(Other definitions for biker that I've seen before include "Rider" , "Hell's Angel?" , "Motorcycist" , "Motorcyclist" .)