Has such opposition given useful aid to two police forces? (9)
I believe the answer is:
diametric
'has such opposition given useful' is the definition.
I can't judge whether this definition defines the answer.
'aid to two police forces?' is the wordplay.
I cannot really see how this works, but
an anagram of 'aid' is 'dia' which is within the answer.
'police' could be 'met' (London Metropolitan Police) and 'met' is found in the answer.
The remaining letters 'ric' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for diametric that I've seen before include "Absolutely opposed to as matricide" , "Completely opposed" , "opposite" .)