Abstract Integration of large amounts of asynchronous renewable energy sources (RES) would reduce the effective inertia of the future Great Britain (GB) network. As a result, after a large infeed loss, containing the grid frequency and limiting its rate of change (RoCoF) above certain thresholds would be a challenge for the system operator. In particular, large RoCoFs could activate RoCoF-sensitive loss-of-mains (LoM) protections of distributed generators (DGs) and trigger cascading disconnections. In this context, thermostatic loads (TCLs) can be controlled to collectively provide support and contribute to the overall system inertial and frequency response. This paper focuses on the transient response period after a frequency disturbance and the fast protection events occurring in this time frame. In particular, this works evaluates the interplay between the local activation settings of LoM protection of DGs and those used to enable the TCL support. This interaction is analysed through a case study on a 36-bus dynamic equivalent of the GB network which shows how local post-fault frequency dynamics drive the overall system response. Results show that TCLs are able to prevent RoCoF-driven DG tripping and reduce the need to adopt high LoM settings, decreasing the risks of maloperation associated with desensitised protections.