The UK just had its hottest night ever recorded with Tuesday temperatures set to surpass 40C.
The Met Office predicts 41C in some parts of England, issuing its first ever red extreme heat warning.
Scotland and Wales will also have their hottest days on record, the Met Office says.
National Rail warned people to travel only if ‘absolutely necessary.’
“There will be delays, cancellations and last-minute changes to train services due to the unprecedented record heat.”
Southern Rail, South Eastern, South Western Railway and GWR have all announced reduced services.
London’s rail network will also see services slashed on Tuesday.
London Luton Airport’s runway has been fixed after the intense heat melted it.
An ‘essential runway repair’ was completed and flights have resumed.