The UK is expected to record the hottest day of the year on Saturday – and forecasters believe it will be even warmer on Sunday.
Met Office experts said the mercury could hit 31C in England and possibly in parts of Northern Ireland, which would beat the 29.7C recorded in south-west London on June 14.
But temperatures could reach 33C in England and south Wales on Sunday as the summer heatwave continues.
Tom Morgan, meteorologist at the Met Office, said temperatures could reach 31C around Yorkshire, the Midlands, south-east Wales and Bristol on Saturday.
He added: “We have got quite an extended hot spell of weather to come through the next several days lasting much of this week, nighttime temperatures will be in the high teens Celsius and daytime temperatures will be in the high twenties or low thirties.
“It’s going to mean that people are really going to feel the effects of the heat as we go through this week.”
The heatwave is breaking records across all of the UK, as the highest temperature of the year was reached across Scotland, Northern Ireland and Wales on Friday, and looks to be beaten again on Saturday and Sunday.
Thousands have flocked to beaches across the country, including Bournemouth beach in Dorset.
For London and the South East to record a heatwave, temperatures must exceed 28C for at least three days, while this drops to 27C in the Midlands and 26C in the South West.
In Northern Ireland, Scotland, Wales, Devon and Cornwall and the North East, it is 25C.
There is also a chance that the highest temperature of all time in Northern Ireland, recorded at 30.8C in Belfast in 1983, could be beaten over the weekend.
The Met Office is working closely with Public Health England over the weekend and has warned people to stay hydrated, not to leave children or pets in cars, and apply sunscreen.
The RAC has also warned drivers to be careful as higher temperatures can cause accidents on roads, which are likely to be busier.
RAC spokesman Rod Dennis said: “With summer weather arriving just as some schools are breaking up, this could turn out to be an extremely busy weekend on the roads – with routes leading to the coasts snarling up as millions get out to enjoy the sun.
“Setting out extremely early could be the only way of missing the inevitable jams, and it might make sense for drivers to make the most of the good weather from home instead.
“For those that do set out, checking their car is road-ready will be vital – or a breakdown in the sweltering heat might result. Tyres, oil and coolant levels should all be looked at before getting behind the wheel.”
PHE also issued a heat-health warning on Thursday for the weekend, urging people to look out for those who may struggle to keep cool and hydrated, such as older people and those who live alone.
People have set up for the entire day on beaches across the nation, with many bringing gazebos, inflatable lilos, and even some tents to enjoy the sun safely.
Surfers and paddleboarders are also enjoying the weather, with many taking to the sea alongside speedboats and dinghies.