Thunderstorms and heavy downpours will herald cooler temperatures across the country following the hottest July day on record.
Forecasters said there would be some respite from the searing heat, which reached a maximum recorded temperature of 36.7C (98F) and caused roads to melt and rail service cancellations.
But parts of south-east England could still see the mercury rise to around 26C (79F) today and the heatwave looks set to continue into the weekend.
Western parts of England and Wales could see heavy showers during the day while hail and lightning struck the North and Scotland overnight, according to forecasters.
MeteoGroup's Nick Prebble said: "Temperatures will be suppressed today, about 10C lower than yesterday with highs of 25C or 26C. It will be noticeably cooler but still warm.
"Friday will likely stay nice and dry across most places and temperatures will be a little warmer, around 27C or 28C, although there will be some unsettled weather Friday night with more thunderstorms, possibly in the south west of England.
"Looking into the weekend, it could top 30C again on Saturday in the South East and London and temperatures will be above average elsewhere too going into Sunday."
Moderate levels of air pollution are expected to remain in the southern and eastern areas of England throughout today and Friday before subsiding over the weekend, according to The Department for Environment, Food and Rural Affairs (Defra)
Earlier it had warned those vulnerable to the effects of pollution to be cautious as the high temperatures caused pollution levels to spike.
Urgent health warnings were issued in response to the heatwave yesterday and paramedics dealt with a surge in calls amid fears the hot weather could result in deaths.
The London Ambulance Service said it had seen call-outs to people fainting increase by more than a third (35%) compared to the same day last week, and a 28% hike in overall calls during the period.
And players at Wimbledon sweltered in the searing heat on courts on the tournament's hottest ever day.
The Met Office said temperatures hit the record high in Heathrow yesterday afternoon - breaking the previous record of 36.5C (98F) set on July 19 2006 in Wisley, Surrey.