Born: a new rule for old PM (5,3)

I believe the answer is:

bonar law

'old pm' is the definition.

'born a new rule' is the wordplay.
'new' indicates anagramming the letters.
'rule' becomes 'law' (law is a kind of rule).
'born'+'a'='borna'
'borna' with letters rearranged gives 'bonar'.
'bonar'+'law'='BONAR LAW'

'for' acts as a link.

I've seen this clue in The Telegraph.

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