So farewell then, Cressida Dick. The Metropolitan Police’s disaster-prone commissioner has finally resigned, with the help of Sadiq Khan. In the view of some people, her police career should have ended in 2005, the day after officers under her direction as “gold commander” executed 27-year-old Brazilian electrician Jean Charles de Menezes on a tube train at Stockwell station, having mistaken him for a suicide bomber. The lethal blunder disgraced the Metropolitan Police worldwide.