The cows would all go dry and most of them would be permanently ruined by mastitus. Battery hens and broiler chickens depend on forced ventilation. Without it they would all die. No doubt the government already has strategic stores of oil in reserve in case of any hitch in oil supplies. But to be of any use they would have to be massive.
Oil is used up by our present system very very quickly.
In the event of war with any power that had any naval capacity, the North Sea, oil rigs would very quickly be knocked out, and oil tankers sent to the bottom. Bring down a pylon on the corner of a line and you cut out that channel for quite a long time. It would be quite impossible to patrol, or guard, thousands of miles of cables which cross high mountains, great woodlands and other empty and desolate places. Issuing out a dole of cash to city people would be an obvious first step, as Jean Gimpel suggests. Most country people have shotguns - few city people do.