The Met Office has released this useful advice if you really need to go out in the wilds. They recommend:

…wear several layers of clothing and keep dry to prevent loss of body heat. Watch out for signs of hypothermia — uncontrollable shivering, slow/slurred speech, memory lapse and drowsiness and frostbite — loss of feeling in and pale appearance of fingers, toes, nose and ear lobes. Keep moving your arms and legs to help the blood circulate.”