He continues to work for southern transport (4)
I believe the answer is:
scab
'he continues to work' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'southern transport' is the wordplay.
'southern' becomes 's' (abbreviation).
'transport' becomes 'cab' (cab is a kind of transport).
's'+'cab'='SCAB'
'for' is the link.
Can you help me to learn more?
(Other definitions for scab that I've seen before include "work when others are out" , "Crust over sore or strike-breaker" , "despicable person" , "Wound's crust" , "Crust formed over wound" .)