A weather warning for extreme heat covering parts of England and Wales has come into force for just the second time.
Temperatures could hit 40C on Wednesday and Thursday in some parts of England and Wales as a “heat-dome” settling over western Europe has brought extreme conditions across the continent.
A red Met Office weather warning for extreme heat covering an area stretching from London to Swansea and Somerset to Birmingham came into force at 9am on Wednesday, and is due to last until 9pm on Thursday.
During the peak of the heatwave on these two days, the temperature could come close to the UK’s all-time high of 40.3C, which was measured in Lincolnshire in July 2022.
The latest heatwave is also expected to surpass the record for June of 35.6C set in Hampshire in 1976.
A combination of extreme heat and humidity could have an impact on public health, infrastructure, power and water supplies, the Met Office said, and could cause heat-related issues for a range of sectors such as transport, energy and water supply.
There could also be an increase in water safety incidents during the heatwave, the agency said, as more people are likely to visit coastal areas, lakes or rivers.
BBC weather forecaster Chris Fawkes said he expected the June temperature record to get “absolutely smashed”, telling the Today programme: “I think this afternoon we’re probably looking at highs reaching around 37C, maybe 38C, so by a big margin we are likely to set a new June temperature record.”
Overnight into Wednesday, temperatures across many areas stayed above 20C, with Brize Norton in Oxfordshire not dipping below 22.3C and Heathrow, west London, not dipping below 22.1C, the Met Office said.
The Met Office launched weather warnings for extreme heat in 2021 after a record-breaking number of heatwave deaths were recorded in England the previous summer.
The first red warning for extreme heat was issued in July 2022.
Red heat health alerts have also been issued by the UK Health Security Agency (UKHSA) for the East of England, East Midlands, London, the South East, the South West and the West Midlands, and amber heat health alerts for the North East, North West, and Yorkshire and The Humber.
These alerts are in place from 1am on Wednesday to 11pm on Thursday, and mean “adverse temperatures are likely to impact on the health and wellbeing of the population”.
On Tuesday the highest temperature logged was 34.6C in Wisley, Surrey, according to the Met Office.
Extreme temperatures on Wednesday and Thursday are expected to cause problems for parents as schools shut early or close to protect pupils amid the heat.
Almost 100 schools in Somerset will be fully closed on both days, according to Somerset Council.
About 100 will be at least partially closed in Buckinghamshire, along with 86 schools in Gloucestershire, according to council data.
Children at some schools have been told they can wear PE kit rather than full school uniform, which can involve long trousers and blazers.
Transport bosses have urged people to avoid travelling on Wednesday and Thursday and are warning those that do to “prepare for a disrupted journey”.
National Rail warned of disruption to Gatwick Express, Great Northern, Southern and Thameslink services until Friday.
Avanti West Coast said it planned to run fewer services than usual between Tuesday and Thursday, and there is “a risk of further disruption”.
Chiltern Railways said it had axed more than half its services until Friday “to ensure the safe operation of the railway”.
Eurostar has cancelled four trains planned to run between London and Paris on Wednesday and Thursday “due to expected adverse weather”.
The AA said its overall workload was up 6% above planned levels on Tuesday, “reflecting increased demand”.
A spokesperson said: “As temperatures remain high, drivers should not underestimate the strain that hot weather can place on vehicles, particularly older cars and those that have not been serviced recently.
“We would encourage drivers to check tyre pressures, coolant and oil levels before setting off and to watch for signs of overheating.
“We also advise occupants to use caution when entering a vehicle in hot weather, as seats, trim and other interior surfaces can quickly reach temperatures that may cause discomfort or minor burns.
“Anyone travelling during the heat should carry plenty of water, keep a mobile phone charged, and ensure they have enough fuel or battery charge in case they encounter delays or become more reliant on air-conditioning than usual, as this can increase fuel or EV charge consumption.
“Preparing for the unexpected can make a significant difference if a breakdown occurs in extreme temperatures.”
The London Fire Brigade has advised people in the capital to keep safe in the heat over the next few days, and be careful with the risk of wildfires and water incidents.
The service urged people to avoid disposable barbecues in parks or open spaces as “they pose a significant fire risk as the heat can be retained for many hours”, and for those having barbecues at home to ensure they are kept “away from flammable materials like fences and sheds”.
NHS trusts across England, including Moorfields Eye Hospital NHS Foundation Trust and Barts Health NHS Trust, have advised people attending appointments during the heatwave to make sure they bring water and check travel beforehand.
NHS advice for how to cope during a heatwave includes keeping out of the heat when possible and cooling down with cold food and drinks, and closing windows and blinds during the day to keep the heat out of living spaces.
The extreme temperatures have also forced the Army to cancel ceremonial operations in London and Windsor, to protect the “wellbeing” of its soldiers.
In a post on X, the Army in London said: “Due to extreme heat this week, Ceremonial Operations in London & Windsor will be changed or cancelled. The wellbeing of our soldiers, horses and the public will always come first.”
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