The Met Office had said people should expect population-wide adverse health affects “leading to serious illness or danger to life”, substantial changes in working practices and daily routine required, high risk of failure of heat-sensitive systems with loss of power, along with transport delays during the heatwave.
A wider amber warning was also in place in Wales, southern England, the Midlands and part of northern England, external, on Thursday, with areas as far north as Manchester expected to see temperatures reach above 30C.
And a separate amber warning for extreme heat, lasting from midnight on Friday, external until 23:59 covers south-east England, eastern England and parts of the Midlands.
The night is expected to be hot and sticky. Temperatures away from northern Scotland will not drop below the high teens and for some in England and Wales will not dip below 22C or perhaps 23C all night.
There could be further records broken by the morning for high overnight minimums.
Warnings are also in force for thunderstorms across Scotland, Northern Ireland,and parts of England and Wales too. These will be fierce but localised.
Friday is another hot day for many but it will feel significantly cooler in Northern Ireland and Scotland.
The worst of the heat and the humidity is likely to move further eastwards and it will feel a little cooler further west.
Within the red warning area temperatures could peak for some at 37C or 38C.
Temperatures in the wider amber warning stretching across the Midlands and East Anglia are still likely to reach the low 30s.
At least six NHS trusts in England have declared critical incidents because of the heatwave, sources have told the BBC.
It comes amid reports the extreme heat has caused problems with IT systems, cancer equipment, lab testing and scanners.
London Ambulance Service said it had recorded its highest ever number of life-threatening emergencies as temperatures soared across the capital “driven by the extreme heat” across the capital.
In Wales, a 50-year-old man died after entering the water at a Welsh beach on Wednesday, South Wales Police announced on Thursday.
The force said they were called to Aberavon beach at around 16:25 to reports of a man needing medical assistance in the water. His death is not being treated as suspicious.
