Heatwave affecting Oakham and Stamford commuters as both the Midland Main Line and East Coast Main Line tracks are at risk of buckling
With temperatures forecast to soar into the high 30s, steel rails could top 50 degrees in the sun – leaving the risk of buckling under pressure.
To protect passenger safety, speed limits are being halved on the Midland Main Line south of Leicester.
This is set to lead to train cancellations, longer journey times and busier services.
The speed limit on the East Coast Main Line will also be halved south of Peterborough.
Rob McIntosh, managing director of Network Rail Eastern, said: “Passenger safety will always be our number one priority.
"And with forecasts of unprecedented temperatures, we have to take action to keep people safe.
“Reducing speed limits will mean fewer services and busier trains on our main routes into and out of London.
“So I’d like to ask all passengers to think about whether their journey is really necessary and, if it is, to make sure they plan well ahead.
“I’m sorry for the disruption this will cause, but it is essential to maintain the safety of the travelling public.”
The speed limit of the Midland Main Line is 125mph in normal circumstances.
But the extreme weather is set to see that limit reduced to 60mph at the southern end of the line.
Train operating companies are working on revised schedules, but there will be significantly reduced services, with longer journey times and the likelihood of overcrowding.
Anyone who has to travel should consult operators for the latest travel information, allow extra time for their journey and carry water with them.
It is hoped services will return to normal on Friday, with temperatures forecast to drop.