The hottest temperature ever recorded in the UK is 38.5 ° C (101.3 ° F), as measured in Faversham, south-east England, in August 2003.
Predictions of the hottest registered day come from Britain scientists call for the designation of heat waves to make public the associated dangers.
"The Met Office must do more to warn people of the dangers of heat waves, and should name heatwaves, as it does in winter storms," said the Grantham Research Institute for Climate Change and the Environment at London School of Economics and Political Science said Tuesday.
"In the UK, far more people have died from the recent heatwaves than from storms, so it should not be disputed to assign both names," said Bob Ward, director of policy at the institute.
He added, "The government and its authorities, including the Met Office, must play a pioneering role in communicating the growing dangers of heat waves and other climate change impacts, so that the British public is better informed and self-protective.
"If this is not the lead of the government, it could also encourage the media to continue to take these risks into account in their reporting, and there will continue to be preventable deaths," warned Ward.
With rising temperatures, the London Metropolitan Police reported on Wednesday that it had found the body of a man who had disappeared swimming with friends on Tuesday in the River Thames in London. The search for two other people who were out of sight while swimming in other parts of the Thames on Tuesday evening continued on Wednesday.
In France, it is expected to be even hotter, and forecasters predict that the heat wave on Thursday will peak with temperatures of 42 C (107.6 F) expected in Paris. On Tuesday, the temperatures in the southwestern city of Bordeaux reached 41.2 ° C, a record for the city.
In preparation for the intense heat, the national weather service Météo France put 80 of its 96 regions on alert.
A red alert – the highest level – was issued in 20 sections. the other 60 are currently in orange alert – the second highest warning level.
"We wanted to warn everyone, and nobody is without risk," said French health minister Agnès Buzyn. "Common sense must prevail, everyone has to feel safe from the red area that this will affect all 20 regions, it's a health alert for all citizens."
Buzyn said the government also encourages companies to allow employees to work from home during the heatwave.
French Sports Minister Roxana Maracineanu previously called for awareness of the high risk of drowning. More than 40 deaths from drowning were registered in the week of the first heatwave summit in late June – an unusually high number, "closely related to heat waves" nuclear reactors in southwest France after exceeding the heat threshold, a company spokesman said.
"We are doing very thorough research on the environment and do not want to harm the fauna and flora. It is a precautionary principle," said an EDF spokesman. "There are big margins to avoid risks."
France registered its highest ever temperature this year on June 29 at Gallargues-le-Montueux in the southern department of Gard.
Chief architect of Notre Dame told Reuters on Wednesday that the record-breaking heatwave could jeopardize the vaulted ceiling of the cathedral, which was hit by a fire in April.
In the meantime In Italy, the country's Ministry of Health has set 15 zones on alert as Europe fights its second extreme heat wave of the summer.
"The heat here today We assume that the heat remains stable until Friday and is expected to increase slightly, "said a spokesman for the Italian Meteorological Service." On Saturday and Sunday a slowdown is expected. "
Further north, Belgium experienced its hottest day of all time with temperatures of up to 39.2 ° C, the highest temperature ever measured in the country, the National Meteorological Service said. The record temperature was reported in Diepenbeek in the eastern province of Limburg.
The World Meteorological Organization defines a heat wave as a period of time where temperatures are at least 5 ° C above average for five consecutive days.
Pedram Javaheri, Antoine Crouin, Mitch McCluskey, Sarah Dean, and Barbara Wojazer of CNN contributed to the report.