English politician holds one small pill for stress (9)
I believe the answer is:
emphasise
'for stress' is the definition.
(I've seen this before)
'english politician holds one small pill' is the wordplay.
'english politician' becomes 'emp' (I can't justify this - if you can you should believe this answer much more).
'holds' becomes 'has' ('have' can be a synonym of 'hold').
'one' becomes 'i' (Roman numeral).
'small' becomes 's' (abbreviation - e.g. clothes size).
'pill' becomes 'e' (ecstasy).
'emp'+'has'+'i'+'s'+'e'='EMPHASISE'
(Other definitions for emphasise that I've seen before include "Place stress on" , "Give extra importance to" , "Mashes pie (anag.)" , "Stress, underline" , "'Stress, accentuate (9)'" .)