DTCEM investigates the scale and complexity needed to approach cyber resilience in IoT- enabled critical national infrastructure (CNI) through the use of digital twins (DT). The emphasis is placed on cyber modelling and simulation approaches to derive technical and operational scenarios for resilience and security testing using a DT. The project seeks to determine the controls and indicators used in system evaluation and explore the efficiencies a DT can offer to develop future security testing scenarios and use cases. Recent changes to the volume and velocity of information have necessitated strong coupling of physical and cyber components, often referred to as cyber-physical systems (CPS). These systems provide faster response times and autonomous component reconfiguration through interaction between sensors and cyber infrastructure. CPS components are subject to technical and operational requirements, from policy to implementation, that determines their ability to maintain resilient operations under disruption. Integration of AI and DT can translate the diverse threat information in these constantly evolving scenarios to actionable intelligence, helping to understand cyber incidents better in the given context. The work examines the efficiencies and challenges introduced from the combination of cyber modelling and simulation using digital twins and state-of-the-art AI-enabled threat source characterisation in building secure and resilient CPS/IoT systems. The research focuses on defining a holistic set of controls and performance metrics (such as security descriptors and threat-related metrics) to evaluate CPS resilience under adverse cyber events through the development and testing of different scenarios. These metrics will be evaluated on selected technical scenarios and operational examples using cyber modelling and simulation and compared to classical state-of-the-art threat source characterisation approaches used in modeling of cyber incidents. This will enable the development of a threat information exchange standard to advance our understanding of how security configuration and practices can be improved when balancing protection and availability in CPS. This project will produce a clear roadmap and proof-of-concept of holistic cyber resilience testing scenarios that integrate cyber standards and security descriptors with emerging modelling techniques to effectively represent the impact of cyberattacks and resilience efforts.