Workmen at last on street work uninterrupted (3-4)
I believe the answer is:
non-stop
'uninterrupted' is the definition.
(I've seen this before)
'workmen at last on street work' is the wordplay.
'at last' indicates one should take the final letters.
'street' becomes 'st' (abbreviation).
'work' becomes 'op' (common abbreviation for 'opus').
The final letter of 'workmen' is 'n'.
'n'+'on'+'st'+'op'='NON-STOP'
(Other definitions for non-stop that I've seen before include "Going straight from A to B" , "Unceasing" , "Uninterrupted" , "Continuous" , "Ceaseless" .)