No, Unionist PM no good for sustaining growth (10)

I believe the answer is:

nourishing

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'sustaining growth' is the definition.
'nourishing' can be an answer for 'sustaining' ('nourish' can be a synonym of 'sustain'). I am not certain of the 'growth' bit.

'no unionist pm no good' is the wordplay.
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'pm' becomes 'rishi' (I am not sure about this - if you are sure you should believe this answer much more).
'no good' becomes 'ng' (abbreviation).
'no'+'u'+'rishi'+'ng'='NOURISHING'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for nourishing that I've seen before include "Nutritious" , "nutritive" .)

I've seen this clue in The Independent.

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