This document sets out sector-wide principles to guide the UK financial system’s collective response to a scenario in which a Global Systemically Important Bank (GSIB) becomes operationally paralysed. Developed by CMORG following SIMEX18, it outlines immediate, behavioural, and planning principles for firms, FMIs, and authorities to coordinate effectively during the first 24–48 hours of such an incident. It includes a GSIB Heat Map to assess systemic impact and substitutability, and highlights the importance of strategic coordination, communication, and pre-agreed contingency planning to maintain market confidence and stability.