Just a few thoughts
From what I've been able to find out: the problem was caused by a gas fired power station in Bedfordshire coming off line, followed two minutes later by a North Sea wind farm aggregation unit failing too. This caused the national power supply frequency to drop from approx 50Hz to 49Hz. This situation is outside allowed tolerances and load has to be shed from the generating system urgently.. I do not know if this is done automatically or by manual intervention or a combination of both. The withdrawal of power from the whole of the Rail Network could in my opinion: be an emergency contingency . We have not herd about cutting of power to steel furnaces/Heavy Industry yet - But situations like this can happen. Remember there's the National Grid (400KV/275KV) and the associated national distribution sistem (132KV/66KV/33KV and 11KV) down to the distribution transformers like the one 150 metres from the house !
I hope there's a proper technically detailed report made available to the public.