PM meeting castaway and cartoonist (5,8)
I believe the answer is:
heath robinson
'cartoonist' is the definition.
(I've seen this before)
'pm meeting castaway' is the wordplay.
'pm' becomes 'Heath' (prime minister Edward Heath).
'meeting' is a charade indicator (letters next to each other).
'castaway' becomes 'robinson' (I've seen this before).
'heath'+'robinson'='HEATH-ROBINSON'
'and' acts as a link.
(Other definitions for heath robinson that I've seen before include "Ingenious and ridiculously over-complicated in construction" , "Ridiculously complex in design" , "Ridiculously complicated in design" , "crazily complicated" , "Cartoonist noted for fantastic machinery" .)