The first weather health alert of the summer has been issued as temperatures are set to soar in parts of the UK.
Peaks of 31C (87.8F) across East Anglia and south-east England are expected on Friday and Saturday.
The Met Office said the main risk to health would come from stifling night-time temperatures of at least 20C (68F) in some places.
“It is the night-time values which are of real concern,” said head of health forecasting Wayne Elliott.
“High humidity and the lack of any breeze could make matters worse for people with underlying health problems.”
‘Feel uncomfortable’
The Met Office’s heat warning is set at level two out of four on its scale of how likely temperatures are to cause health problems.
Those at most risk from the hot weather are the elderly and babies and young children.
To keep cool, the NHS advises wearing loose cotton clothes, spraying or splashing faces and the backs of necks with cold water several times a day and staying in the coolest rooms of the house as much as possible.
Windows should be kept closed when the room is cooler than it is outside.
BBC weather forecaster Carol Kirkwood said: “We’re not just talking about the temperatures by day, we’re also talking about the minimum temperatures because for some of us they’re not going to dip lower than 18C – and that will feel uncomfortable.”
Hosepipe ban
Temperatures will be more bearable in north-west England, west Wales, Scotland and Northern Ireland, reaching the high teens and low 20s centigrade over the weekend.
The highest temperature of the year so far was 30.9C (87.6F) at Gravesend in Kent on 27 June.
Pet charity the Blue Cross has issued advice for owners about keeping their animals safe in the hot weather, warning that they can suffer fatal heatstroke within minutes.
The organisation said pets should never be left alone in a car, even with the windows open, and exercising during the heat of the day should be avoided.
Meanwhile, a hosepipe ban started at 0600 BST on Friday affecting millions of householders in parts of Cumbria, Greater Manchester, Lancashire and Merseyside.
Water company United Utilities said the region had had the driest start to a year since records began in 1929.
