Sudden move due to a desire to get on from town? (6)
I believe the answer is:
twitch
'sudden move' is the definition.
(sudden twitch in the body)
'a desire to get on from town?' is the wordplay.
'a desire' becomes 'itch' (itch is a kind of desire).
'to get' means one lot of letters go next to another.
'from' is a deletion indicator.
'town' with 'on' taken out is 'tw'.
'itch' put after 'tw' is 'TWITCH'.
'due to' acts as a link.
(Other definitions for twitch that I've seen before include "Start" , "pluck" , "Uncontrolled, jerky motion" , "Nervous jerk or tic" , "Quiver or jerk spasmodically" .)