Ah, not nearly as intimately as you, but given that London is such a bustling [read: "full of criminality"] city... [It's hard never to have dealings with the police.]
[A small shrug. And a touch apologetically:] Of course, the dutiful policemen all work hard and to their best abilities. [He shouldn't be too critical, is what he means. Sherlock has more of a leg to stand on there.]
What is it that you teach, if I may? The school is admittedly not a part of this world I have explored much.