Metropolitan Police officers carry out a raid on a property on the Churchill Gardens estate in Pimlico nearly 5,000 officers must be brought in between now and 2017 just to keep the force’s numbers steady because of retirements. Photograph: Getty

John Kent was a man before his time. In Carlisle in 1837, Kent, the son of a West Indian servant, became the first known black police constable in Bri(...)