Video report by ITV News Correspondent Martha Fairlie
A new weather record was set in west London on Saturday as temperatures soared to 34C - making it the hottest day of 2019.
The Met Office said the record-breaking readings were taken at Heathrow and elsewhere in west London.
It said this was just short of the 35.6C June record set in the notoriously hot summer 1976. The new record smashed the previous 2019 record, set on Friday in Achnagart in the Scottish Highlands as the mercury peaked at a sweltering 30C.
The warmer weather will continue over the coming days. It will be hottest across the south, into the Midlands and as far north as Lincolnshire.
Read more: Is the heatwave: A one day wonder?
Emergency services across the country have shared advice to stay safe, cool and hydrated during the hot conditions - and warned against swimming in open water, after three people in the UK drowned in recent days.
The RSPCA has also urged people to call 999 if they find a dog left alone in a car. In Essex, firefighters had to rescue a dog trapped in a car on the top floor of a multistorey car park.
Glastonbury reassures campers over fears of water shortage
Glastonbury organisers have moved to reassure music fans over rumours of a water shortage, issuing a statement on Saturday afternoon stating there is not a lack of water on site.
It warned of long queues at some of the free water taps on site, asking people to find quieter parts of the festival zone to gather water. It also said it was restricting access to showers in a bit to conserve supplies.
In addition to free tap water, the festival has been providing free sun lotion.
People urged to check on elderly and vulnerable
England's most senior nurse has called on people to take precautions - and in particular, to help children, the elderly and other vulnerable people at risk of being affected by the heat.
Ruth May, chief nursing officer for England, said: "Whether you're going to be out in the garden like me or heading off to Glastonbury, it's really important to take simple precautions like drinking plenty of water, using high-factor sunscreen and remembering to take allergy medication if you need it - as is making sure to check in on neighbours and loved ones who can suffer the most from heat and pollen."
According to NHS England almost 3,000 people were admitted to hospital because of heat-related ailments in 2017/18, including 632 with severe sunburn, 100 cases of heat exhaustion and 223 cases of sun and heat-stroke.
Why is it so hot?
The rising heat is in part due to warm air originating from northern Africa that has brought a scorching heatwave to a large swathe of Europe.
Southern France has been placed on an unprecedented red alert, with the country recording its hottest day ever, and firefighters in Spain battle wildfires on a scale not seen for 20 years.
MeteoFrance said Villevieille in the southern region of Provence reached 45.1C (113.2F) on Friday afternoon, France's hottest ever temperature since records began.
Government officials have urged caution and a warning that the worst could yet be to come.
The red alert in France signifies a “dangerous weather phenomenon” and is the first since the system was introduced in 2004 following a 2003 heatwave that led to 15,000 premature deaths.
The Sahara-style heatwave spreading over parts of Europe has been caused by an “enormous” reservoir of warm air and has been linked to the deaths of three swimmers on south coast beaches in France.
Warning against cooling off in rivers and lakes after teenager death
Three people have also died in the UK.
On Thursday, two men, aged 25 and 26, died in Torquay after getting into difficulty in the sea.
Speaking on Friday, Det Insp Andrew Naismith, of Greater Manchester Police's Bury district, warned people against swimming in open water to cool off in the heat.
"This is an incredibly tragic incident in which a young girl has lost her life, and my thoughts are with her family at this devastating time," he said.
"With the warmer weather, it's tempting to go into the water to cool off, but I'd like to remind everyone of the dangers of playing near or swimming in rivers, lakes and reservoirs and would strongly urge against this."
The heatwave could be short-lived for Britain however, as Saturday was predicted to bring some thunderstorms and isolated showers for Northern Ireland, northern parts of England and Scotland.
And big change is expected on Sunday on the back of westerly winds from the Atlantic Ocean, with sunny spells predicted across the UK to be interspersed with showers.