Digital Twins (DT) are abstract, data-dependent and data-driven models. They are used to model the state of a physical component or system. This facilitates failure warnings and allows continuous improvement activities to be undertaken. As a result, DTs can be used as part of operational safety management. However, DTs also provide a tantalising opportunity to model whole systems before implementation, establishing a baseline model from which to identify safety and safety management issues relating to system realisation and operational safety management. They facilitate comparison between this model and reality as system realisation progresses. This study considers the use of DT in this role. Can the use of DTs mitigate issues that often delay the introduction to service? Can they be used early in the lifecycle to propose and check the credibility of ‘approval-in-principle’ documentation to ensure issues are discovered early rather than late in the project lifecycle? Benefits range from the application of change controls, impact assessment and the identification of interfaces and dependencies. This work sets out an approach to Systems and Safety Engineering using ‘Engineered DTs’ as part of safety assurance of current and future phases of a safety-critical project.