Look sharp as terrible cheats caught out underpinning manufacture (4,5)
I believe the answer is:
make haste
'look sharp' is the definition.
(to look sharp is to make haste or hurry up)
'cheats caught out underpinning manufacture' is the wordplay.
'cheats' becomes 'has' (I've seen this before).
'caught out' becomes 'te' (I am not sure about this - if you are sure you should believe this answer much more).
'underpinning' says to put letters next to each other (I've seen this in other clues).
'manufacture' becomes 'make' (I've seen this before).
'has'+'te'='haste'
'haste' put after 'make' is 'MAKE HASTE'.
'as terrible' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for make haste that I've seen before include "Hurry, don't be slow" , "Festina lente - . . . . . . . . . slowly" , "Shake mate to hurry up" , "speed" .)