Hot weather prompts Met Office heatwave health alert
The first weather health alert of the summer has been issued as temperatures soared in parts of the UK.
Temperatures peaked at 31C (87.8F) in Gravesend, Kent, on Friday and similar temperatures are expected in south-east England on Saturday.
The Met Office said the main health risk would be stifling temperatures at night of20C (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."
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, 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.
Temperatures reached 30C in Suffolk and Heathrow airport.
BBC weather forecaster Peter Gibbs said: "Temperatures will be staying close to 20C in London and in the high teens in large towns and cities overnight. It will become more humid as the weekend continues, which will make it feel a bit more uncomfortable."
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 previous highest temperature of the year was 30.9C (87.6F) also in 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.