Unknown heads of test and trace member of ruling party backed - lousy! (5)
I believe the answer is:
nitty
'lousy' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for nitty that I've seen before include "___-gritty, the basics" , "lousy" , "Gritty's partner?" .)