There is no single law which prohibits fraud
There is no single law which prohibits fraud. What lawyers call 'fraud law' is in reality covered by a mixture of different offences and common law (evolved and established legal principles). They range from offences covered by the theft act to the new offences of the Fraud Act 2006. There are, of course, financial and company offences which do not necessarily fall into the fraud category, but which are often also present in fraud investigations and proceedings.
