Tony Blair, not heartless yob, may be appearing before a judge (2,5)
I believe the answer is:
on trial
'tony' is the definition.
Both the answer and definition are adjectives.
Perhaps you can see a link between them that I don't see?
'blair not heartless yob may be appearing before a judge' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'not' is 'ont' which is within the answer.
'a' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for on trial that I've seen before include "Undergoing court process" , "Subject to being found satisfactory" , "Undergoing scrutiny" , "In court to answer charge, in the dock" , "being judged" .)