Development of Marine Autonomous Systems (MAS) has accelerated sharply in recent years. Government, academia and industry papers advising on the future of the maritime sector unanimously agree on the need for a regulatory framework to be established to enable the safe development, testing and operation of MAS. A regulatory framework must be developed which does not introduce constraints on the growth of MAS capabilities. This paper analyses the existing maritime regulations and proposes necessary changes to guide a process to develop regulatory requirements. Regulation development guidelines include a range of considerations including technical, legal and insurance/liability, where adherence is complex the development of an alternative MAS specific regulation or an explanation of how the existing regulation may be complied with by MAS is required. The proposed process links MAS technical capabilities to appropriate testing regimes and associated supporting bodies of evidence and recommends testing regimes which combine simulation with demonstrations and real-world tests and leading to demonstrable levels of safety. Establishing a regulatory framework for MAS is a challenging task, but a key enabler to the effective adoption of autonomous vessels in the maritime sector. Through proposing changes to the current process and a new approach for MAS, this paper aims to take tangible steps in developing a regulatory solution.