The Met Office has issued a red warning for extreme heat in London and north of England, whilst an amber warning remains in place for south.
"This means there is a substantial risk of disruption to the train service,” according to Govia Thameslink Railway, which runs Gatwick Express, Great Northern, Southern and Thameslink trains
Due to the ‘extremely hot weather’, people are being asked to ‘only travel if necessary’ on Monday (July 18) and Tuesday (July 19).
Most Popular
A spokesperson added: “Thameslink and Great Northern will be running a significantly reduced service across all routes with speed restrictions in place.
"Trains that do run will be busy and travel is expected to be disrupted with a high chance of incidents that cause cancellations.
“Cancellations are also expected on Southern due to speed restrictions and further disruption is highly likely on the day.”
Gatwick Express services will not run but Southern services will run in their place making extra stops.
Govia Thameslink Railway Chief Operating Officer Angie Doll said: “Please think carefully about your options and travel only if absolutely necessary on Monday and Tuesday.
“With the Met Office issuing warnings for extreme heat, speed restrictions are being put in place across our network to keep trains and passengers safe.
“This means we’ll have far fewer services for people to catch and there will also be at very real risk of substantial disruption. Even if you are able to travel in the morning, you may need to consider alternative ways to get home as a result.”
Trains listed in online journey planners such as www.nationalrail.co.uk will be updated on Sunday for Monday’s travel and on Monday for Tuesday.
Jake Kelly, Network Rail’s system operator group director, said: “Rail passengers in England and Wales should only travel if necessary on Monday and Tuesday as there will be delays and cancellations to train services due to the unprecedented heat we’re expecting.
“The wellbeing of our passengers is our first priority so we’re asking all passengers who decide to travel to take time to prepare before leaving the house. Remember to bring a water bottle with you, along with whatever else you need to keep yourself well in the heat.