The Met Office has issued an “amber extreme heat warning” for a wide area including Brighton and Hove
And the UK Health Security Agency has issued a “level 3 heat health alert”, in force from today (Tuesday 9 August) until Sunday aimed at health and care professionals.
The agency is advising people to look out for those who are vulnerable, including older people, young children and anyone with underlying health conditions.
Daytime temperatures are expected to hit the high eighties in the coming days, with a forecast of 88F (31C) on Thursday, Friday and Saturday.
Experts have warned about the potential effects on health, transport and infrastructure, as well as on pets, especially dogs.
The Met Office said: “High pressure is dominating this week, with fine and dry conditions across most of the country, prolonged sunshine and light to moderate breezes.
“Temperatures will rise from warm or very warm to locally hot in most regions, with a focus of the warmest weather in central to southern England.
“Headline maximum temperatures will reach the mid-thirties, most likely on Friday or Saturday.
“The biggest uncertainty is over the end of the hot spell, with thundery showers expected to arrive from the south through the weekend introducing cloudier, somewhat cooler conditions.
“Confidence in the details of these showers remains low, however, with potentially a continuation of warm or very warm temperatures into next week for some areas before we see a gradual return to around average.”
National Highways head of road safety Jeremy Phillips said: “It is always very important to plan ahead for your journey and this advice remains the same during periods of hot weather.
“When hot weather is forecast, please remember to take plenty of drinking water with you – enough for you and your passengers.
“We also advise everyone should check their vehicles, such as tyres, coolant and oil levels, before heading out.”
British Veterinary Association president Justine Shotton said: “While it’s wonderful to make the most of the warm weather, please don’t forget to give some extra attention to pets, many of whom may struggle as the temperature rises.”
Dr Shotton said: “Animals need extra care during the summer to keep them safe from heat-related illnesses such as heatstroke, heart conditions, breathing difficulties and sunburn, many of which can sadly be fatal.
“Make sure animals have access to fresh drinking water, good ventilation and shade from direct sunlight at all times.
“Dogs especially can overheat easily so make sure they aren’t walked or exercised in the hottest parts of the day or left inside a hot car or conservatory for even a little while.
“Keep an eye out for early signs of heatstroke, such as heavy panting, drooling, restlessness and lack of co-ordination and contact a vet immediately in case you have any concerns.”
The UK Health Security Agency’s head of extreme events Agostinho Sousa said: “Temperatures will feel very warm again this week, particularly in southern and central parts of the country.”
Dr Sousa added: ““We want everyone to enjoy the warm weather safely. But remember that heat can have a fast impact on health.
“It’s important to ensure that people who are more vulnerable – elderly people who live alone and people with underlying health conditions – are prepared for coping during the hot weather.
“The most important advice is to ensure they stay hydrated, keep cool and take steps to prevent their homes from overheating.”