It has been the UK's hottest day of the year so far after temperatures reached 31C (87.8F) at Heathrow airport, according to Met Office figures.
They topped the previous high of 29.9C recorded at Edenfel, County Tyrone in Northern Ireland last Monday.
The soaring temperatures saw shoppers spend thousands of pounds on the high street and online, buying barbecues, food, sunscreen and garden furniture.
But the heat has prompted warnings from health authorities urging the public to take care in the potentially "dangerous" heatwave conditions.
And the hot spell shows no sign of ending with temperatures set to remain in the mid-to-high 20s well into next week.
A warning issued by the Met Office was escalated to a level three alert for Yorkshire and the Humber on Saturday, while level two alerts were in place across most of England.
"Heatwaves can be dangerous, especially for the very young, very old or those with chronic diseases," the alert said.
A spokesman for Public Health England (PHE) said: "Level two alerts are triggered as soon as the Met Office forecasts that there is a 60% chance of temperatures being high enough on at least two consecutive days to have a significant effect on health.
"This will normally happen two to three days before a heatwave is expected to occur. As most deaths occur in the first two days, this is an important stage at which to ensure readiness and swift action to reduce harm from a potential heatwave."
Wisley in Surrey recorded a temperature of 30.5C (86.9F) followed by 29.2C (84.5F) in Usk, Monmouthshire, south east Wales.
Sunday is expected to be another scorcher with possibly slightly lower top temperatures and there is no sign of Britain's summer being rained off.
South-west England is the only area with a level three alert in place for Sunday, which "requires social and healthcare services to target specific actions at high-risk groups," according to the Met Office.
Dr Angie Bone, head of the PHE's Heatwave Plan, said: "Everyone can enjoy the sun safely by keeping out of the heat at the hottest time of the day, avoiding sunburn and staying hydrated with plenty of cool drinks.
"The elderly and those with long-term illnesses are particularly vulnerable to the effects of very hot weather, so it's important to look out for them and keep indoor areas as cool as possible."
More than 11 million motorists are planning to hit the road this weekend, according to the RAC.
Popular spots include the Lake District, Devon and Cornwall, the south coast of England, and Yorkshire.
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