Unleaded pinchbeck kept in a controlled environment (2,5)
I believe the answer is:
in check
'unleaded pinchbeck kept' is the definition.
I can't judge whether this defines the answer.
'in a controlled environment' is the wordplay.
'a controlled environment' becomes 'check' (I can't justify this - if you can you should give a lot more credence to this answer).
'in'+'check'='IN CHECK'
Can you help me to learn more?
(Other definitions for in check that I've seen before include "Under control" , "Restrained" , "State of chess king under direct attack" , "Attacked" .)