Up to a third of trains across the South and South-East could be cancelled tomorrow as the heatwave peaks.
Train companies are preparing emergency timetables to cope with record numbers of speed restrictions amid predictions of 38C temperatures.
A Network Rail source said: “There is a significant risk of rails buckling tomorrow and we have to take every safety precaution.
There will be a lot of speed restrictions in place but we could see a third of trains cancelled across the South tomorrow.”
Rail track temperatures in direct sunlight can often be up to 20C higher than the air temperature.
Because rails are made of steel they expand in the heat and can sometimes curve and buckle. Running trains at slower speeds helps reduce the track temperature.
Speed limits as low as 20mph were in place today. A Southeastern spokesman said: “Significantly fewer services will be running tomorrow and many trains will be much busier as a result.
"Those trains which do run will take longer to complete their journeys, particularly on longer distance routes.”
Speed limits were in place today on services between West Hampstead and Kentish Town, Shepherd’s Bush and Wembley Central, and Sutton loop services around Mitcham Junction. More limits were set to be ordered this afternoon, delaying journeys home.
Meanwhile, RAC spokesman Rod Dennis warned motorists: “People shouldn’t be too surprised to see the surfaces of roads and pavements [melting]. It is also vital that drivers check their vehicles are ready for the hot weather.”
