A line of Metropolitan Police officers “took a knee” in tribute to George Floyd today as thousands of protesters gathered outside Downing Street. At least 15,000 Black Lives Matter protesters including actor John Boyega and singer Liam Payne gathered in London, ignoring social distancing guidelines, as a show of anger against the death of Mr. Floyd in the US. And at least 2,000 of those demonstrated in front of Downing Street, shouting “take a knee” at Metropolitan Police officers guarding security gates. Four officers obliged, to the approval of the crowds, who urged other officers to follow the example of...