English football is facing up to one of its biggest crises of modern times as the Mark Clattenburg affair threatened to explode into another bitter racism saga.

Clattenburg's fight to clear his name over allegations of using "inappropriate language" towards Chelsea stars John Obi Mikel and Juan Mata witnessed a new twist on Tuesday when police launched a formal investigation into the matter.

The Metropolitan Police confirmed they had acted on a "complaint" from the Society of Black Lawyers after the European champions accused referee Clattenburg of using comments understood to have been interpreted as racist in the club's acrimonious defeat to Manchester United on Sunday.

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