With the temperature set to soar into the high 30s tomorrow, speed restrictions will be in place on trains across Hertfordshire.

To protect passenger safety, speed limits are being halved on the East Coast Main Line south of Peterborough.

Network Rail has said these safety measures are likely to lead to cancellations, longer journey times and busier services on the network.

The forecast of the unprecedented conditions could see steel rails topping 50°C in the sun, leaving them at risk of buckling under pressure.

Managing director of Network Rail Eastern Rob McIntosh 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 East Coast Main Line is 125mph in normal circumstances. 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 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.