The cartoonist sacked with little warning (2,5,6)
I believe the answer is:
at short notice
'with little warning' is the definition.
(I've seen this before)
'the cartoonist sacked' is the wordplay.
'sacked' indicates anagramming the letters.
'the'+'cartoonist'='thecartoonist'
'thecartoonist' anagrammed gives 'AT SHORT NOTICE'.
(Other definitions for at short notice that I've seen before include "With little time for preparation" , "With little advance warning" .)