Firm initially monitors scheme to import island's beef (8)
I believe the answer is:
Here is my best explanation:
'beef' is the definition.
'firm initially monitors scheme to import island's' is the subsidiary indication.
'firm' becomes 'co'.
'initially' indicates taking the first letters.
'scheme' becomes 'plan'.
'to import' means one lot of letters goes inside another.
'island' becomes 'i'.
The first letter of 'monitors' is 'm'.
'plan' going around 'i' is 'plain'.
(Other definitions for complain that I've seen before include "Grumble, moan", "Grizzle", "Express a sense of injury or say you're ill", "Grumble, grouse", "Express dissatisfaction", "Grouse, grumble", "Express a grievance", "Bellyache", "Beef (or grouse?)" and "Remonstrate".)