Rail passengers travelling between London and Brighton are being warned of delays due to the hot weather expected on Monday and Tuesday.
Temperatures could climb to 34C (93F) in the South East on Monday, and even higher on Tuesday, with an amber heat health alert in place.
Network Rail said the soaring temperatures would make the track temperature about 50C (122F), leading to blanket speed restrictions and a revised timetable.
Anyone using the Brighton Main Line commuter route is being urged to check the National Rail website before setting off.
Timetables are also available on the websites of operators, Southern, Thameslink and Gatwick Express.
A spokesman for Network Rail said: “We’re sorry but this means we won’t be able to run as many trains as normal and journeys will take longer.
“Trains that are running will also be much busier. If you are able to work from home then that may be your best option.”
