Speed to the North (3)

I believe the answer is:

ton

'speed' is the definition.
(I've seen this before)

'to the north' is the wordplay.
'the north' becomes 'N' (abbreviation).
'to'+'n'='TON'

(Other definitions for ton that I've seen before include "Twenty cwt" , "Two thousand, two hundred and forty lbs avoirdupois" , "Heavyweight" , "A slangy 100 mph - heavy" , "Fashionable" .)

I've seen this clue in the Evening Standard.

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