Today was the hottest day of the year so far with temperatures set to rise even further, forecasters said.
Tennis fans were near the centre of the heatwave as crowds sweltered at the All England Club in Wimbledon ahead of Andy Murray's clash with Stanislas Wawrinka this afternoon.
The Met Office confirmed today is already the hottest day of the year so far, with nearby Charlwood, near Gatwick in Surrey, recording a temperature of 28.4C (83F).
Previously the hottest day was last Thursday at Heathrow at 28C (82.4).
Paul Knightley, a forecaster for Meteogroup, the weather division of the Press Association, said: "London was pushing 28C over the weekend, and today we are getting close to 30 degrees (86F) in the London area."
He said the heatwave was likely to last until Thursday or Friday, with the mercury rising even higher over the coming days.
Helen Chivers, a spokeswoman for the Met Office, said: "Thursday looks like it will be the hottest day of this spell."
Temperatures in the capital are the same as Athens in Greece, and higher than Lisbon in Portugal (27C, 80.6F), Nice in France (25C, 77F) and Rio de Janeiro in Brazil (23C, 73.4F).
Eastern areas were the hottest, while the South West and Wales were the most likely to be hit by thunderstorms.
Although many enjoyed the sunshine, there were warnings of the dangers.
People in the capital were being urged by the London Ambulance Service to take extra care.
As the heat soared to almost 28C over the weekend, the service took 10,605 calls on Saturday and Sunday - an increase of nearly a fifth on the previous weekend.
Emergency incidents included large numbers of patients treated for breathing problems (489, up from 369), chest pains (461, up from 412), loss of consciousness and fainting (437, up from 364).
Jason Killens, deputy director of operations said: "Hot weather can be very dangerous for the young, older people or those with serious illnesses.
"With the temperatures set to be high over the next few days, our priority will continue to be to respond to patients who are seriously ill or injured."
A 'heat health' warning has been issued by the Met Office for this week, and night temperatures in some areas may not drop below 18 degrees celcius (64.4F).
Those not at work may be taking advantage of the sunshine at parks, outdoor pools and beaches around the country, but the sea can be dangerous and the Royal National Lifeboat Institution (RNLI) is encouraging beach-goers, particularly swimmers, to be careful.
Kelly Keating, beach safety programmes manager for RNLI, said: "Our key advice for people planning a trip to the beach, especially those planning to go in the water, is to choose a lifeguarded beach and swim between the red and yellow flags, where the lifeguards can see you."
"Protecting yourself form the sun is also really important. We recommend people remember SLIP, SLAP, SLOP - slip on a T-Shirt, slap on a hat, slop on some suncream. Drinking plenty of fluid is also vital as the sun and wind can easily dehydrate you."
With the hot weather could come thunderstorms, and Mr Knightley advised how people can stay safe if they get caught in a storm.
He said: "You shouldn't stand under a tree, if people hear thunder try and get inside or in a car.
"People shouldn't think they're immune to it, you can lessen the risk by not being out in the first place. A car is the best place to be."
A man was recovering at home today after being airlifted to hospital when he got into trouble in the sea in Wales yesterday.
Weak swimmer Tom Merrick, 23, from Haverfordwest in Dyfed, Wales, was taken to Withybush Hospital in a rescue helicopter after struggling off Broadhaven beach.
He tried to follow Poppy Whitlock, also 23, and from Haverfordwest, to Church Rock, and she raised the alarm after getting back to the beach.
Two other men from Haverfordwest, Robert Skinner and Matthew Gilles, both 23, got into difficulty, but were not taken to hospital.
Mark Clark, a spokesman for the Maritime and Coastguard Agency, said: "The sea can be very dangerous if you are a weak swimmer or not particularly competent in that sort of swimming.
"The sea shouldn't be treated like a swimming pool. The water currents and tides are stronger than anybody's strength. The sea has to be treated with the utmost respect."
Motorists were also warned of the dangers of driving in the high temperatures.
The AA advised people to carry at least one litre of water per person, as well as a container for pets.
Stewart Topp, AA patrol of the year, said: "Driving in this heat can be pretty uncomfortable if you're not properly prepared.
"You can dehydrate quickly, so make sure you carry plenty of drinking water.
"Take sun hats and high factor sun lotion too, as if your car breaks down, there is often no shade at the roadside."
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