Focus BBC magazine crossword

[3rdjay]

I will try another one of these obscure clues.
Police check to find a level of proof(6,4)
Thank you so much -- if I can finish one corner!

[baitress]

copper test. Used to test urine content

[pmh1wheel]

Looks more like breath test to me

[TheWinner]

I think Breath Test too.

[kettledrum]

It rather depends on whether it's a cryptic crossword or not. A policeman is a 'copper'.

[kettledrum]

On reconsideration .... I've just looked up copper test & it seems to have nothing to do with alcohol, so I think it must be breath test !

[baitress]

Hi kettledrum.
Can you please tell me where in the clue
is there any reference to alcohol. It merely
asks for a level of proof.copper fits the police
part and test fits the check part.
So copper test finds a level of proof for
urine content.

[pmh1wheel]

Alcoholic proof is a measure of how much ethanol there is in a drink. This one is less cryptic, more joke. Besides, copper doesn't fit with any of the answers going down