Following predictions from the met office of freezing weather conditions in Britain this winter, the mayor of London has warned that this could be the worst winter since 1962, when Britons shivered in sub-zero temperatures from the end of Dec until April. The met has issued an amber alert to emergency services to prepare for the worst. A weather phenomenon known as the North Atlantic Oscillation (NAO) is the basis for the alert the difference in atmospheric pressure between the Azores and Iceland can determine whether Britain will have a warm, wet winter or an icy one. The fact that the United Kingdom is no longer self-sufficient in North Sea gas has led to fears that gas shortages could result in energy cuts, as gas is diverted to heating and away from business and industry. The national health service also faces a major challenge as prolonged icy weather could mean a shortage of hospital beds. Older people are particularly at risk because of inadequate heating in their homes.