BackgroundTo address the large wintertime health burden in England, the Department of Health introduced a Cold Weather Plan (CWP) in 2011, which provides advice to relevant organisations and the general public on actions that should be taken to protect vulnerable individuals during cold weather. The Department of Health commissioned the Policy Innovation Research Unit at the London School of Hygiene and Tropical Medicine to undertake an assessment of the implementation of the CWP over winter 2012–13 and to begin to assess its potential health benefits and costs. MethodsThe research consisted of time-series regression and episode analysis of historic records of daily mortality, 1993–2006 (from the Office for National Statistics) and emergency hospital admissions and accident and emergency department visits, 1997–2010 (both from the Health and Social Care Information Centre), linked to weather data for each region of England. Models were adjusted for seasonal factors unrelated to temperature and possible day-of-week effects. Semistructured telephone interviews (n=52) with staff involved in the implementation of the CWP were done in ten local authorities selected from within regions of the country with different winter weather patterns to provide a spread of urban versus rural areas and levels of socioeconomic deprivation. Interviews focused on the operational policy changes and health-care or social-care services' response to the introduction of the CWP for comparison with the expectations contained in the plan. 25 local authority managers, 13 National Health Service (NHS) commissioners, four NHS acute or community trust managers, two NHS ambulance trust managers, six care home managers, one family doctor, and one voluntary sector manager were interviewed, dependent on the local allocation of responsibility for CWP implementation between agencies. Analysis of CWP-related plans and related documents in the ten local authority areas was done. A national survey was undertaken of 8500 community nurse members of the Royal College of Nursing, of whom 437 (5%) responded. Semi-structured telephone interviews (n=35) with individuals at high risk from cold weather exposure living in their own homes in two local authorities were also done. People were interviewed shortly after a level 3 cold weather alert had been issued, which is issued when severe winter weather is occurring. FindingsCold-related effects were noted for both mortality and hospital use but the biggest cold burdens occurred at temperatures outside the alert thresholds used in the CWP. Effects could be delayed by up to 4 weeks after initial exposure. The CWP and the cold weather alerts were viewed as a helpful exposition of good practice by local health-care and social-care managers. The CWP formalised existing activity and helped to coordinate the actions of a wide range of staff in different agencies. There were examples of innovations that local staff attributed directly to the CWP (eg, a push to raise influenza immunisation levels of front-line staff). Analysis of the interviews with people living in the community suggested that interventions aimed at people who are vulnerable to cold should focus on people who live in cold homes and are socially isolated. InterpretationThe CWP is broadly welcomed and has the potential to reduce cold-related public health effects and health services usage, but the alerts may need revision. The present study is limited by the fact that the most robust quantitative evidence on the effectiveness of the CWP will only come once there are sufficient years after intervention to assess any changes in weather–health relations. FundingDepartment of Health Policy Research Programme.