By around 1800, the first well-known investigators in England were not paid as police officers but rather, were paid a percentage of all fines resulting from successful prosecution of thieves. These investigators soon became known as:

Answer: The Bow street runners

Explanation: From History, The Bow street runners emerged as the first set of professional London police having stated as a group of 6 members in 1749 before rising to 68 members by 1800. They made use of sticks, handcuffs and pistol in apprehending criminals. The Bow street runners were paid a certain percentage of the fines accrued from successful conviction of criminals. The Bow street runners were later disbanded in 1839 and succeeded by the Metropolitan Police Service.