The Royal Mint was responsible not just for the production of new coinage, but for the protection of the existing coins from clippers and forgers. When Newton became Warden of the Mint in 1696, he took it upon himself to prosecute these crimes. It was a role for which he was surprisingly well-qualified. His alchemical researches meant that he had a practical knowledge of smelting that rivalled that of any forger. His history of research and feuding stood him in good stead as a detective and prosecutor of criminals. His dedication to this role - for which he received no reward in addition to his basic salary - rapidly made him the terror of the underworld. And, unexpectedly for a man who just five years previously had seemed destined to live out his life in academic isolation, he turned out to have a genius for creating a network of informants and contacts.

Ironically, one of his biggest obstacles was the strength of his legal powers. Although the government had good reason to regard clipping as a threat to the nation - and it therefore carried the death penalty as an act of Treason - individual clippers and forgers rarely dealt with more than half a dozen coins at any one time, and their profits were small. So there was a reluctance to hand people over to draconian justice. Added to that, the reward for information was a generous £40, which meant that a very high percentage of the informers were people prepared to turn over others to their deaths, rather than public-spirited citizens seeking to do right by their country. And finally, it was far from unheard of for less-than-honest citizens to 'turn in' entirely innocent rivals or enemies. All of this meant that a case had to be rock solid to ensure a conviction from a jury.

Newton - Scourge of the Underworld

Newton was as ruthless in hunting down criminals as he was in his scientific and personal vendettas. He knew that he needed more than just testimony from a witness; he needed at least two or three witnesses to overcome juries' reluctance to convict. One of his favoured methods was to incarcerate his suspects in the notorious Newgate Prison with cell-mates whom he knew would report their conversations back to him. These could then be used as corroborating witnesses in court or - better - used to extract a confession. Using inmates' fear of execution to extract information from them was another favoured tactic; in one case, he offered a series of 13 stays of execution to one man, none of them longer than two weeks but all of them paid for with information about his accomplices and underworld acquaintances.

Newton also used less underhand methods. He had himself made a Justice of the Peace in seven counties so that he could pursue his quarries should they flee the city. He would concentrate on finds of false coins and trace them back to their source. And he had a network of informers unlike any that had been seen before in English domestic policing.

Chaloner

Newton's most famous case was that of William Chaloner, who was the closest thing that London had to a criminal mastermind. From an apprenticeship as a destitute nail-maker unable to ply his trade in guild-dominated London, he had risen to a wealth and social status where he could even advise Parliament on the economic crisis. By being careful never to be directly associated with the actual act of forgery himself, Chaloner had made prosecution very difficult, and Newton was forced to arrest and release him several times before finally getting a conviction. Finally, Chaloner wrote a personal letter to Newton (the tone could perhaps have been a little more pleading given the circumstances, rather than indignant that his trial was invalid on a technicality) pleading for mercy. Newton did not respond, and Chaloner was duly hung, drawn and quartered.