Scorching temperatures saw the UK officially record its warmest day of the year so far after a heat health alert was issued.
The Met Office said that at 2.46pm on Wednesday the thermometer reached 32.6C (90.7F) at London’s Heathrow Airport.
In Northolt in west London and Kew Gardens in the south-west of the capital, the temperature hit 31.5C (88.7F).
Elsewhere, in Chertsey, Surrey, the heat rose to 31.3C (88.3F), and in South Farnborough, Hampshire, a temperature of 31.1C (88F) was recorded.
Updated temperatures for the day are expected later.
Forecasters expect temperatures to reach around 33C (91.4F) in some parts of the country and people are being warned to take care in the sun.
The Met Office raised the level to three on Wednesday, as health authorities encouraged those most vulnerable – many of whom have been shielding during the lockdown – to protect themselves amid the “exceptionally hot weather forecast this week”.
Public Health England (PHE) said older people, those with underlying health conditions, and very young children were all more at risk from the higher temperatures.
The amber level three, which is currently in place for the West and East Midlands, requires social and healthcare services to target specific actions at high-risk groups, according to the Met Office website.
People have been advised to keep cool and stay hydrated where possible.
The mercury is expected to hit the low-30s in the south of England before Friday and warnings have been issued about UV levels, which are going to be “exceptionally high” over the next few days.
Emer O’Connell, consultant in public health at PHE, said it was important that people kept checking on the vulnerable, as many continued to spend more time at home due to coronavirus.
“You will need to do things differently this year, for example keeping in touch by phone,” she said.
“If you need to provide direct care to someone at risk from hot weather, follow Government guidance on how to do this safely.
“The most important advice is to ensure they stay hydrated, keep cool and know how to keep their homes cool.”
Health minister Jo Churchill said people could take simple steps to keep themselves safe.
She said: “Apply sunscreen regularly, stay hydrated, and protect your head from the sun.
“Look out for those who are vulnerable in the heat, and provide support where needed, continuing to follow social distancing guidance.”
Advice from the Met Office included closing curtains on rooms that face the sun to keep indoor spaces cooler, avoiding excess alcohol and dressing appropriately for the weather.
St John Ambulance said this could mean wearing light clothes to keep your skin covered and protected in the sun, as well as wearing high-factor sunscreen.
Shoppers have also been advised to be aware they could be forced to spend extra time in the sun as a result of social distancing measures.
Dr Lynn Thomas, medical director at St John Ambulance, said: “You could end up in the sun for longer than expected on what would normally be a quick journey, such as queuing to enter the supermarket, so you should be prepared to look after yourself and others.”
She added: “Heat exhaustion and heatstroke are two of the most serious problems that can develop when the mercury soars but by being prepared you can spot the early warning signs, such as headache and dizziness.”
Dog owners have been urged to avoid exercising their pets during the hottest part of the day.
Vets Now, a provider of emergency veterinary care, warned that the average survival rate of a dog diagnosed with heatstroke is only 50%.
The RSPCA said it had received 330 calls in regard to animal welfare and the hot weather since March 23, adding it was expecting “hundreds more” as temperatures increase this week.
The public is also being reminded to take care around water throughout the summer, amid concerns people might be tempted to take a dip to cool down.
A search is ongoing for a man missing after he is believed to have got into difficulty in water at Lulle Brook in Cookham in Berkshire on Tuesday evening.
Police said one man, aged in his thirties, was in a serious condition in hospital after being brought to safety by a member of the public.
London Fire Brigade (LFB) has warned people not to have barbecues on dry grass, not to drop cigarettes or matches, and not to leave rubbish such as glass bottles lying around amid a risk they could start fires.
Met Office meteorologist Alex Burkill said UV levels would reach eight across many places and get up to nine across parts of Devon and Cornwall.
He said: “That’s about as high as it gets really in the UK.
“The sun is as strong as it gets at the moment because we’re so close to the solstice.
“We’ve got peak sun strength, clear skies, plenty of sunshine – it’s the perfect ingredients for high UV.”
Beaches have been busy this week as people take advantage of the good weather after months of lockdown.
Tuesday was not quite the hottest day of the year, as the 28.6C (83.5F) recorded at Heathrow Airport and Kew Gardens fell short of the 28.9C (84F) recorded at the end of May.
Concern has been expressed that increase in the alert level might have come too late for many of most vulnerable.
Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change and the Environment, said: “The Government has so far failed to amend the Heat-Health Watch Service so that it provides better protection for people who are particularly at risk from the effects of heat this summer.”
Earlier this year a study, led by the London School of Hygiene and Tropical Medicine, of the heatwave plan for England found that most deaths and hospital admissions associated with heat happen outside periods when the alert system is triggered.