Trains across the UK were cancelled on Wednesday as extreme heat struck the country.
The news comes as passengers were told to avoid non-essential travel in areas covered by the Met Office’s red warning.
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.
The red warning for extreme heat covers an area stretching from London to Swansea and from Somerset to Birmingham, from 9am on Wednesday until 9pm on Thursday.
Network Rail warned there would be “significant disruption” across England and Wales as it imposes speed restrictions to minimise the risk from heat-related issues such as buckled rails and sagging overhead electric wires.
A combination of extreme heat and humidity could impact public health, infrastructure, power and water supplies, the Met Office said, and cause heat-related issues for a range of sectors such as transport, energy and water supply.
Passengers are advised to travel before midday if possible, and carry a water bottle.
Those with a ticket for a service on Wednesday or Thursday are being allowed to travel earlier in the day – when the temperatures are lower – or on Friday.
If they no longer want to travel, they can get a full refund without paying a fee.
Online journey planners are not showing correct timetables until the day of travel because of short-notice cancellations.
Train performance website trains.im shows 11% of services across Britain were either cancelled or delayed by more than half an hour as of 7.30am on Wednesday.
A week ago the figure was 4.7%.
Avanti West Coast was the operator with the most disruption on Wednesday morning, with four out of five service either cancelled or more than 30 minutes late.
Chiltern Railways said it is running fewer than half its usual services until Friday “to ensure the safe operation of the railway”.
This affects London Marylebone services to and from Birmingham, Oxford and Aylesbury via Amersham.
Great Western Railway issued a plea for its services to be used for “essential travel only” on Wednesday and Thursday.
It said speed restrictions mean it will be forced to run fewer services than usual and journey times will be extended.
It is also running fewer trains than normal between London Paddington and Reading because Network Rail is not moving some points – pieces of metal that enable trains to change tracks – on the route to cut the risk of failures, which are more likely in high temperatures.
LNER said “we strongly advise that you do not travel” on Wednesday or Thursday.
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 Wednesday and Thursday, according to Somerset Council.
And around 100 schools will be at least partially closed over the next two days 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.
Read MoreUK drivers risk £110 fines for keeping cool in cars during heatwave
London Euston trains cut amid railway track ‘buckling’ fears during UK heatwave
Trains cancelled as passengers warned to only travel ‘if necessary’
‘Why am I doing fingerprints every time?: Readers baffled by new EU entry rules
Crew member dies after falling off cruise ship in Hebrides
Flights suspended from UK airport after thunderstorms damage air traffic control
