An amber “heat health watch” is still in place for parts of England, with people being warned to try and stay out of the sun between 11am and 3pm.
The mercury hit a high of 31.4C (88.5F) on Tuesday, with temperatures expected to edge above 33C (91.4C) today.
And it could be about to get even hotter.
Friday could be the hottest ever July day, with the Met Office saying the record high of 36.7C recorded in 2015 could be broken.
Amid the scorching conditions, the Royal College of Nursing (RCN) has warned that dehydration on hospital wards is a health risk which can lead to serious conditions, including urinary tract infections and acute kidney injury.
It said lots of hospitals are not designed with hot conditions in mind, with many not fitted with air conditioning.
Some nurses have also complained of being unable to stay sufficiently hydrated because their hospital does not allow water bottles in clinical areas, the RCN said.
Anna Crossley, RCN professional lead for acute, emergency and critical care, said: “Nursing staff should not be expected to work 12-hour shifts in stifling heat with no access to water.
“Not only is this extremely uncomfortable, it is dangerous – both for them and the patients they care for.
“Dehydration also affects cognition, which could lead to mistakes.
“Hospital management should allow water bottles on shift so staff can stay hydrated and make sure they have breaks. This is an issue of patient safety.”
Thunderstorms are forecast on Friday, which will provide some much welcome relief from the heat.
Torrential downpours are predicted to hit parts of the UK, with as much as 30mm (1.2in) forecast to fall in just an hour in some areas.
A thunderstorm warning is in place for eastern and northern parts of England from Friday afternoon and the rain could be accompanied by hail and strong winds, which means the temperature could drop down to the high 20s.
The Local Government Association said social workers, community wardens and maintenance staff remain on high alert to identify those who could be struggling in the heatwave.
Meanwhile, pet owners have been told to avoid exercising their dogs and other animals during the hottest parts of the day because of the risk of burnt paws on scalding pavements and the prospect of heatstroke.
The RSPCA has also warned dog owners not to leave pets in hot cars.
Farming leaders have warned crops are being affected by the hot weather, with harvests beginning early in many places following the driest first half of summer on record.
Reservoirs for watering vegetables are running dry and livestock owners are being forded to use winter feed because the summer grass has withered away, they said.