Survivors

[Phil]

Seems to me that with only 12500 people left alive in the country one of your most important aims should be to establish friendly relations with everyone you can locate.
Anthropological studies show that for a tribe to be able to self sustain without getting in new members the tribe needs 872 members.
Your best bet would be putting up notices on all main roads imo.
Regarding plague we don't have a reservoir of it in this country, so very unlikely to have it here if there was a collapse.Fleas leave a dead body once it gets cold,as they can no longer drink the blood.
The suggestion that there is a rat within 20 feet of everyone is a none starter when you think about it,if it were so then you'd see them every day of your lives.I last saw one in the garden 5 years ago as it died,from .177 poisoning.
I think that we probably wouldn't be able to restart the nation with only 12500 survivors.