The forecast of hot temperatures across the country this week has prompted the first Heat-Health Watch warning this summer.
Parts of England will see temperatures climb to highs of 30°C by day, but a key factor will be the night-time temperatures. Lows in some areas may not fall below 18°C.
The Met Office has triggered the Heatwave Plan alert level 2 on behalf of the Department of Health (DH), which means the risk that high temperatures being reached in one or more regions on at least two consecutive days, and the intervening night, is 60%.
London, the East of England, South West, South East and the Midlands are the most likely to be affected.
Head of Health Forecasting at the Met Office, Wayne Elliott, said: "We have been working closely with the DH to develop this service, which is aimed at those vulnerable to high temperatures, especially the elderly.”
The last time a heat-health warning was issued was in the hot summer of 2006.
The Heat-Health Watch is expected to increase to level three during the course of the week. Even though England will see the highest temperatures, all of the UK will have some very warm weather, with the continuing chance of thunderstorms in a few places leading to high rainfall totals locally.
The DH has warned social and healthcare services to ensure readiness to reduce harm from a potential heatwave.
The heat is especially dangerous for the very young, older people or those with serious illnesses. In particular, it can make heart and respiratory problems worse. In extreme cases, excess heat can lead to heat stroke, which can be fatal.
A DH spokesperson said: “Keeping the home as cool as possible during hot weather and remembering the needs of friends, relatives and neighbours who could be at risk is essential.
“The elderly and those who are ill, are particularly vulnerable during hot weather and the most oppressive conditions occur in our towns and cities.”