Following the advent of Industry 4.0, there have been significant benefits to industrial process optimisation through increased interconnectivity and the integration of Information Technology (IT) and Operational Technology (OT). However, this has also led to an increased attack surface for cyber threat actors to target. A growing number of cyber attacks on industrial environments, including Critical National Infrastructure, has, subsequently, been observed. In response, government and standardisation organisations alike have invested considerable resources in improving the cyber security of these environments. This includes response and recovery, often used as a last line of defence against cyber attacks. However, due to the unique design philosophies of Industrial Control Systems (ICS), several challenges exist for effectively securing these systems against digital threats.

Through an analysis of standards and guidelines, used for assessing and improving cyber incident response and recovery capabilities, and stakeholder engagement on the implementation of these in practice, this thesis first identifies the challenges that exist when it comes to preparing for cyber incidents targeting ICS/OT environments. In particular, risk management, which involves identifying, evaluating, and prioritising risks and finding solutions to minimise, monitor, and control these, was found to be essential for improving preparation for cyber incidents. Assurance techniques are used as part of risk management to generate evidence for making claims of assurances about security. Alongside this, adversary-centric security tests such as penetration tests are used to evaluate and improve cyber resilience and incident response capabilities by emulating the actions of malicious actors. However, despite the benefits that these provide, they are currently not implemented to their full potential due to the safety and operational risks that exist in ICS/OT environments.

This thesis contributes to academic and industry knowledge by proposing a framework that incorporates methods for identifying and quantifying the safety and operational risks of conducting adversary-centric security tests within ICS/OT environments. In understanding the risks, these engagements can be scoped using precise constraints so as to maximise the depth of testing while minimising risk to safety and the operational process. The framework is then evaluated through a qualitative study involving industry experts, confirming the framework's validity for implementation in practice.