One southern port in Hampshire (7)

I believe the answer is:

andover

I'm a little stuck... Click here to teach me more about this clue!

'in hampshire' is the definition.
(I know that Andover located in the administrative territorial entity Hampshire)

'one southern port' is the wordplay.
'one' becomes 'an' (an apple is one apple).
'southern port' becomes 'dover' (port town in Kent. I am not sure about the 'southern' bit.).
'an'+'dover'='ANDOVER'

Can you help me to learn more?

(Other definitions for andover that I've seen before include "Hants town" , "New town development" , "Town in Hampshire" .)

I've seen this clue in the Evening Standard.

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