Older, especially over 75 years of age. Children, especially under 4 years of age. Live alone and/or socially isolated. Long-term health condition (particularly heart and breathing problems). On multiple medications. Reduced mobility and/or ability to look after themselves. Difficulty adapting their behaviour in warmer weather (for example, due to dementia or alcohol/drug misuse issues). At home during the hottest part of the day (for example, small children or home workers).