Old PM in Wilson or Thatcher (5)

I believe the answer is:

north

'old pm' is the definition.
(Lord North, 18th-century prime minister)

'in wilson or thatcher' is the wordplay.
'in' says the answer is hidden in the clue.
'NORTH' is hidden within 'wilson or thatcher'.

(Other definitions for north that I've seen before include "Boreal; South's opposite" , "Magnetic or true?" , "British leader" , "A quarter" , "Former PM" .)

I've seen this clue in The Times.

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