No, it is not a legal requirement to have a written agency agreement in place, although it is often the case that a written agency agreement clarifies the rights, duties and obligations of both agent and principal, which assists in determining the contractual relationship between them.  Both agent and principal have a right to receive from the other a signed written document setting out the terms of the agency contract, on request.  Often, however, it will be in an agent’s interests not to have a written agreement in place.