Nobody else at work up here, not surprisingly (4,5)
I believe the answer is:
none other
'nobody else' is the definition.
(I've seen this before)
'at work up here not surprisingly' is the wordplay.
'at work' becomes 'on' (on can mean activated or working).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'on' reversed gives 'no'.
'here'+'not'='herenot'
'herenot' with letters rearranged gives 'neother'.
'no'+'neother'='NONE OTHER'
(Other definitions for none other that I've seen before include "Nobody else" , "Just the one" .)