I find it reassuring that the national grid are taking this seriously and preparing, rather than simply hoping for the best.
If key staff are to live on site, I hope that proper consideration has been given to avoiding infection from one worker to another. Any form of shared dormitory accommodation is most unsuitable in present conditions.
Caravans, motor caravans, or modular buildings with plenty of fresh air between units would be more suitable. Even a large and well constructed tent per person, are IMO far preferable to bunk beds in a store room, again due to the ample fresh air between one tent and another.
For emergency on-site housing, key workers with large families or long commutes should be given priority. Those who live alone and within a short drive of work are clearly lower risk.