Dynamic virtual organisations (VOs) can arise in situations in which it is critical that they continue to operate, even in sub-optimal environments. Models of information flow in dynamic VOs are therefore needed in order to permit the rigorous verification of resilience properties before commitments are made to implementation. This paper proposes a refinement-based modelling approach for the design and analysis of VO policy resilience. The approach is demonstrated by using the refinement-based formalism Event-B to model a VO structure, commonly referred to as the Bronze/Silver/Gold structure that frequently arises in multi-agency response to emergencies. Machine-assisted proof is used to compare the validity of alternative information flow policies in Bronze/Silver/Gold when a fault is induced in the VO structure.