Britons will face temperatures of at least 35C by Thursday, weather forecasters warned, as parts of the country remain in the grip of a stifling heatwave.

Weeks of high temperatures – predicted to exceed 30C all this week in some places – have turned fields brown, ripened wild berries months earlier than normal and triggered an amber-level heat health warning, with people urged to stay out of the sun.

At midnight following the hottest day of the year on Monday, East Anglia and London residents struggled to sleep in 21C heat, equivalent to the average July daytime temperature for the regions.

Becky Mitchell, a meteorologist from the Met Office, warned that the mercury “could go even warmer than” the expected 35C on Thursday, however.

The soaring temperatures come courtesy of warm air arriving from France combined with high pressure across the country.

The hottest July day on record is 36.7C, recorded at Heathrow in 2015.

Central and south-eastern England, including London, remain under the heat health warning. Amber is the second-highest level before a red “national emergency”.

Ultra-violet levels are high, the Met Office said, telling people to stay in the shade during the middle of the day, wear sunscreen and cover up.

It came as a survey revealed nearly three-quarters of parents do not protect their children’s eyes from UV rays. Thirty-one per cent believe eyeballs cannot be sunburned.

UK weather: Temperatures soar as heatwave intensifies Show all 35 1 /35 UK weather: Temperatures soar as heatwave intensifies UK weather: Temperatures soar as heatwave intensifies People on the beach at Croyde Beach in North Devon PA UK weather: Temperatures soar as heatwave intensifies People enjoy the sun at Carsington Water in Derbyshire PA UK weather: Temperatures soar as heatwave intensifies Sophie Todd, aged 7, and her mother Jane Todd playing in one of the Trafalgar Square fountains in London PA UK weather: Temperatures soar as heatwave intensifies A couple play catch with a ball whilst swimming in the River Stour Getty Images UK weather: Temperatures soar as heatwave intensifies Children play in the fountains at Granary Square, King's Cross PA UK weather: Temperatures soar as heatwave intensifies A dog under an umbrella at the Festival of British Eventing at Gatcombe Park, Gloucestershire PA UK weather: Temperatures soar as heatwave intensifies People sunbath on the clifftop at Woolacombe Beach in North Devon PA UK weather: Temperatures soar as heatwave intensifies A woman stands in a field of sunflowers at Vine House Farm near Spalding, Lincolnshire PA UK weather: Temperatures soar as heatwave intensifies A woman takes a selfie in front of St Paul's Chathedral PA UK weather: Temperatures soar as heatwave intensifies Paddle boarders off the coast at Tynemouth , Tyne & Wear PA UK weather: Temperatures soar as heatwave intensifies People on Woolacombe Beach in North Devon PA UK weather: Temperatures soar as heatwave intensifies A canal boat passes along the Regent's Canal PA UK weather: Temperatures soar as heatwave intensifies People relax in the warm weather on the beach in Brighton PA UK weather: Temperatures soar as heatwave intensifies People enjoying the hot weather and sunshine on the banks of the River Thames in Putney Rex Features UK weather: Temperatures soar as heatwave intensifies Spectators enjoy the hot weather during day seven of the Nature Valley International at Devonshire Park PA UK weather: Temperatures soar as heatwave intensifies Hot and sunny day in Hyde Park's Serpentine lake Rex UK weather: Temperatures soar as heatwave intensifies People relax in the warm weather on the beach in Eastbourne PA UK weather: Temperatures soar as heatwave intensifies People sunbathe as they enjoy the warm weather on Bournemouth beach PA UK weather: Temperatures soar as heatwave intensifies A person sunbathes on a blow up mattress in the sea off of Bournemouth beach in Dorset PA UK weather: Temperatures soar as heatwave intensifies A couple relax in the sunshine on the beach in Brighton PA UK weather: Temperatures soar as heatwave intensifies People play in water fountains in the Queen Elizabeth Olympic Park in east London PA UK weather: Temperatures soar as heatwave intensifies Chris Bryant from Basingstoke paddle boards at Boscombe Beach in Dorset PA UK weather: Temperatures soar as heatwave intensifies People shelter from the sun beneath umbrellas as they walk in St James's Park in London AFP/Getty Images UK weather: Temperatures soar as heatwave intensifies Arianna Espiritu Kelly, 2, eats an ice-cream in the Queen Elizabeth Olympic Park PA UK weather: Temperatures soar as heatwave intensifies Victor the Polar Bear enjoys a dip in the water at Yorkshire Wildlife Park PA UK weather: Temperatures soar as heatwave intensifies People on the beach in Brighton PA UK weather: Temperatures soar as heatwave intensifies Woman relax in the sunshine on the beach in Hastings, Sussex PA UK weather: Temperatures soar as heatwave intensifies People enjoy their lunch break in the sunshine near Tower Bridge in London PA UK weather: Temperatures soar as heatwave intensifies Police horses drink from a water fountain during the hot weather in Green Park PA UK weather: Temperatures soar as heatwave intensifies Anglers fish on New Brighton beach on the Wirral, Merseyside as the sun rises over the Port of Liverpool and the River Mersey PA UK weather: Temperatures soar as heatwave intensifies A family of lemurs enjoy an ice lolly at Yorkshire Wildlife Park PA UK weather: Temperatures soar as heatwave intensifies People enjoy the sunshine in St James's Park in in London AFP/Getty Images UK weather: Temperatures soar as heatwave intensifies A duck swims in the algae covered lake in St James's Park, London PA UK weather: Temperatures soar as heatwave intensifies A couple cycle in the sunshine around Bewl Water in Kent PA UK weather: Temperatures soar as heatwave intensifies A man takes a break in the sun on Southbank, London PA

Children’s eyes do not fully develop and provide natural lens protection until the age of 12 and they are likely to spend much more time outside during school holidays than their parents.

Despite this, only 30 per cent of parents said they worried about their children having too much exposure to UV and how it could lead to long term damage.

However, pollen count was low across the UK, the Met Office said early on Tuesday. “Although we are now into weed #pollen season, it’s likely to take a while for the pollen levels to rise again,” it tweeted.