I've always worked that a method statement outlines the task from A to B, the safe system of work is how to control high risk aspects of the task. E.g. fitting container doors - method statement will be tools, personnel and the actual steps of the task, however use of a hydraulic jack carries specific risks and therefore a safe system of work will outline the particular risks and how the person is protected from those risks.

I'm bound to be contradicted though ;-)