Spike Milligan's last seen in short programme (5)
I believe the answer is:
prong
'spike' is the definition.
(I've seen this before)
'milligan's last seen in short programme' is the wordplay.
'last' indicates one should take the final letters.
'seen in' is an insertion indicator.
'short programme' becomes 'prog' (short for programme; 'short' indicates an abbreviation).
The last letter of 'milligan' is 'n'.
'n' placed within 'prog' is 'PRONG'.
(Other definitions for prong that I've seen before include "one gets stuck into dinner" , "Spike of fork etc" , "tip?" , "Fork part" , "Spur; projecting part" .)