The UK heatwave has broken a 59-year record for most consecutive 34C days.
The Met Office confirmed temperatures had reached 34.6C in central London on Wednesday, marking the first time since at least 1961 there had been six consecutive days of 34C and above.
The mercury has consistently been high since the end of last week.
On Tuesday afternoon the hottest temperatures were recorded at Heathrow, Yeovilton and Bedford.
The extreme heat has led to flash flooding in parts of Wales, with more thunderstorms predicted across the UK later this week.
Forecasters have warned there will be four days of thunderstorms across the UK in the coming days.
On Monday, the whole of Wales was covered by a yellow thunderstorm warning as it was hit by severe flash flooding.
Met Office forecaster Bonnie Diamond said: “Parts of the UK will see some very heavy thunderstorms with torrential rainfall and a chance of flash flooding from Wednesday – this could result in landslides and problems with travel.
“Yellow thunderstorm warnings will remain in place until Sunday, affecting most of the UK.”
Temperatures will remain high in the south of the country until the end of the week.
Diamond added: “Temperatures should remain in the mid-20s to low 30s and will be above the heatwave threshold in the south of England until Friday.”
Some unlucky households in Sussex have been left without water since Friday due to high demand during the heatwave.
They have been without a water supply due to low pressure caused by more people and businesses running their taps.
Specialist water tankers have had to be brought in, along with bottled water stations to help the desperate residents.
South East Water said the shortage is due to the extreme demand in water as temperatures soared.
The water company added that more people taking “staycations” was "putting a strain" on the country’s water network.