The Met Office on Tuesday extended its Amber Weather Warning for “extreme heat” in most of England and parts of Wales.
The warning was previously issued to cover July 17, it has now been extended to cover Monday.
The Met Office said temperatures will rise later this week and over the weekend, likely peaking on Sunday and Monday, but may last into Tuesday in places.
Temperatures are predicted to soar into the 30s, with a 30 percent chance of seeing the hottest day on record for the UK, beating the existing high of 38.7C in Cambridge in 2019.
Britons are warned over potential “population-wide adverse health effects” that may lead to “serious illness or danger to life.”
The Met Office also cautioned people about water safety incidents as “significantly more people” are expected to visit beaches, lakes, and rivers.
It also said possible delays and closures should be expected on roads, as well as delays and cancellations to rail and air travel, with potential for “significant welfare issues” caused by the delays.
The Met Office says the mercury is predicted to rise to 30C in some parts of the South East on Tuesday while the rest of England is expected to see temperatures rise to the high 20s.
The whole of England is largely expected to experience sunny days with some cloud cover over the next week to match the temperatures of mid to high 20s.
It will cool off a little on Thursday and Friday, with the North West and North East of England predicted to have some rain.
Temperatures are expected to be over 35C in the South East on Sunday, and overnight temperatures will also be very warm.
Parts of Wales will see temperatures of more than 32C on Sunday and Monday.
Households are being urged to save water as the temperatures push up demand after months of dry weather in some areas.
Water companies said they are not planning to restrict water usage at the moment, but some are warning that groundwater and reservoir supplies are lower than average following low rainfall this year.
In a press release issued on Tuesday, industry body Water UK called on people to save water by turning off the taps when brushing their teeth or washing dishes, avoid running half-empty dishwashers, using watering cans instead of garden hose, reusing paddling pool water for plants, letting the lawn go brown, and not washing cars.
Network Rail is preparing to implement speed restrictions in the coming days to reduce the likelihood of tracks buckling, and councils are planning to use gritters to spread sand on melting roads.