Former Blue Peter presenter wearing vest? (9)
I believe the answer is:
singleton
'wearing vest?' is the definition.
(singlet on - type of vest)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for singleton that I've seen before include "spinster or bachelor?" , "One of a kind" , "Stolen gin (anag.)" , "Card that is only one held in its suit" , "in club, maybe, all alone" .)