UK heatwave: July heat record may be broken
The Met Office told the BBC to expect highs of 37C, meaning the record of 36.7C, set in 2015, may be beaten.
The heat has already led to travel issues with both the Eurotunnel and Network Rail reporting disruption.
The public are also being urged to take care while swimming after police were called to incidents in rivers, lakes and piers across England.
"Unprecedented" high temperatures have been blamed for delays to cross-Channel rail services leaving customers waiting for more than five hours in 30C heat.
Air conditioning problems meant some carriages could not be used, which led to the delays, Eurotunnel said.
Eurotunnel suggested people cancel trips if they were able to and warned that ferry companies "do not have the availability take any of our customers".
Forecasters had said the UK's all-time record of 38.5C could be passed on Friday, but those estimates have been toned down following overnight storms.
More storms are expected from 14:00 BST, with a yellow weather warning issued for the east of England.
The current heatwave could become the new normal for UK summers by 2040 because of climate change, MPs say.
The Environmental Audit Committee warns of 7,000 heat-related deaths every year in the UK by 2050 if the government doesn't act quickly.
Higher temperatures put some people at increased risk of dying from cardiac, kidney and respiratory diseases.
The MPs say ministers must act to protect people - especially with an ageing population in the UK.
Scientists differ on whether the current global rash of heatwaves is definitely caused by climate change.
But all agree that future heatwaves will be hotter and more frequent thanks to carbon emissions.
The MPs highlight a warning from the Met Office that UK summer temperatures could regularly reach 38.5C by the 2040s. ■