This probably will be the toughest question to answer. If you are just beginning out, you may be running routine investigative operations and you could earn £ 10,000 to £ 20,000 a year. If you are thoroughly knowledgeable about the legal provisions and are able to handle corporate investigation, you may earn £ 100,000 or more a year. Your earnings are dependant on several factors, including the complexity of cases you have solved.