Upstanding prime minister regularly spat out (6)
I believe the answer is:
asleep
'out' is the definition.
(out can mean unconscious or asleep)
'upstanding prime minister regularly spat' is the wordplay.
'upstanding' is a reversal indicator.
'prime minister' becomes 'peel' (Robert Peel).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'spat' are 'sa'.
'peel'+'sa'='peelsa'
'peelsa' backwards is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "Please (anag) - numb" , "Conked out" , "not paying attention" , "(Of a limb) numb" , "See, pal strangely is not awake" .)