Thursday could see the UK's all-time record temperature broken, as temperatures could reach as high as 39C.
In central and eastern parts of England, heatwave thresholds are expected to be met as high temperatures last throughout the middle part of this week.
Important advice from Public Health England and Port of London
Met Office forecaster Luke Miall said temperatures in London are expected to reach 38C (100.4F) on Thursday and which would pass the current record for a day in July which stands at 36.7C (98.1F) recorded at Heathrow Airport in 2015.
He added: “There is now a 40% chance of going over the UK temperature record of 38.5C (101.3F) which was recorded in Faversham, Kent, in August 2003.”
Overnight temperature were around 24C overnight on Wednesday, making it difficult for some to sleep.
Here's what you need to know about how to cope in the unseasonably hot weather.
What's the best ways to stay cool and safe during a heatwave?
NHS UK has published a number of tips which you can utilise to keep cool.
Shut windows and pull down the shades when it's hotter outside
Open windows when cooler to allow for ventilation
Avoid the sun during the hottest part of the day (usually between 11am and 3pm)
Have cool baths or showers
Drink plenty of water
Wearing a hat in the sun can help keep you cool and help you avoid getting heatstroke
Cars can get hot so try to ventilate them
Wear sunscreen with a higher SPF factor to avoid sunburn
Stay tuned to weather forecasts
When planning to travel, check the forecast at your destination
Who is most at risk during the hot weather?
Some people are more susceptible to a heatwave than others.
Those more able are encouraged to check up on loved ones who may struggle during a heatwave.
Among the most vulnerable include:
Older people, particularly those over 75
Babies and young children
People with long-term health conditions, particular those who have heart or breathing problems
Those with mobility issues
People who suffer with mental health problems
People who abuse drugs or alcohol
Physically active people or those in the sun - for example, labourers and people doing sport
Animals can also be at high risk. Pet owners are urged not leave dogs in cars as sweltering temperatures can kill
Isn't the weather supposed to be like this?
Typically in July, London would be seeing temperatures of 23C - so forecast highs of 36C would be 13C higher than average.
Scotland averages 17C, while Wales typically is about 19.2C.
Northern Ireland may also be basking in above average temperatures, rather than the July norm of 18.5C.
Remember to stay safe
It can be tempting to go for a swim in a local lake or river to cool down during a heatwave.
Hundreds of visitors were evacuated from the family attraction just outside Cirencester as police, fire and ambulance crews search the water.
Police divers recovered a body at about 8.50pm.
Swimmers have been advised to remember to beware the dangers of drowning during what could seem like a casual dip.
Last year, 255 people died as a result of accidental drowning, including seven children under the age of nine.
A particular risk can be cold water shock, which is one of the biggest causes of drowning – temperatures in seas, rivers, canals and lakes can be a low as 15C in summer, around half that of swimming pools.
The Local Government Association says people should only swim in water “that is clearly marked as safe and under the control of a lifeguard”.