With temperatures set to soar into the mid 30s this week, train companies are warning that the heat could interfere with Britain's rail network.
Commuters are being told to check their journeys ahead of time for ristricted services, as the heat is predicted to get so fierce that it could buckle rails.
"As rails are made out of steel, they expand as they heat up and are subject to strong compression," Network Rail said on its website.
"This expansion has to be managed to reduce the risk of track buckling. If the track does buckle, the line must be closed and the track repaired before services can resume, causing considerable disruption."
First Great Western services in the Thames Valley area will be subject to speed restrictions from midday to 8pm today - meaning there will be fewer fast trains.
Cooler temperatures are forecast after thunderstorms and heavy downpours hit parts of Britain after the hottest July day on record.
After a sweltering day, where temperatures reached a record high for July, the weather turned.
Paddling pools, ice creams and sun hats were among just some of the ways people kept cool during the hottest July day ever recorded.