Totally clean? Not you, no way, Mr Johnson (7)

I believe the answer is:

premier

'johnson' is the definition.
(as in Boris Johnson, UK prime minister)

I can't explain the remainder of the clue.

(Other definitions for premier that I've seen before include "Foremost" , "First in importance" , "First - head of government" , "First (minister)" , "Earliest" .)

I've seen this clue in The Guardian.

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