With record temperatures in London predicted today, Network Rail is advising passengers to expect significant disruption on services to and from London Liverpool Street.
The rail infrastructure company says: "In warm weather, track can become up to 20 degrees hotter than air temperature. The forces exerted by trains passing over such track at speed could prompt the rail to buckle, potentially causing a derailment or, at the least, significant delays.
"As slower trains apply lower forces on the track, speed restrictions of 60mph will be introduced during the hottest part of the day - between 12pm and 8pm - on the Great Eastern and West Anglia main lines.
"As a result, fewer trains will be able to run across the network, with Greater Anglia, Great Northern, TfL Rail and c2c all running revised services. Many trains will be much busier than usual, and it is likely to take longer for passengers to complete their journeys.
"We are also planning to minimise the impact that heavier freight trains have on the rails by not running freight services between 12pm and 5pm today.
"We're sorry for the disruption these speed restrictions will cause, but I hope you'll understand that they are essential to keep everyone safe"