Lancashire town immediately north? (7)
'lancashire town' is the definition.
(I've seen this before)
'immediately north?' is the wordplay.
'immediately' becomes 'presto' (synonyms).
'north?' becomes 'N' (synonyms).
(Other definitions for preston that I've seen before include "Town on the Ribble", "English city", "Town in Lancashire", "city (as of 2002)", "Administrative centre of Lancashire".)