With the predicted extreme temperatures making the headlines on every news bulletin, local people are being warned by South Western Railway to only travel if absolutely necessary today and tomorrow.

Temperatures are expected to reach up to 40°C in London and the surrounding area, and the mid 30s in the western parts of the network. As rail temperatures can be up to 20°C higher than the air around them, there is a risk of them buckling in the extreme heat.

As a result, Network Rail will introduce speed restrictions to minimise the force on the tracks and reduce the chance of buckling. These speed restrictions will, in turn, make journeys longer and SWR will introduce a reduced service on Monday and Tuesday in a bid to give customers certainty on what will run.

People with tickets for travel on its services on Monday and Tuesday will be permitted to travel on Wednesday and Thursday instead.

The speed restrictions will particularly affect the mainline services, with long-distance services to Exeter, Salisbury, Bournemouth, Weymouth, Southampton and Portsmouth most likely to be impacted.

Service changes are likely to appear in journey planners at short notice, so anyone who chooses to travel despite the warnings is urged to check their journey before setting off and to expect last minute delays and cancellations.

Customers are also urged to carry water with them, to cover up and to wear sunscreen when travelling.

SWR’s customer experience director, Christian Neill, said: “These unprecedented temperatures will pose a significant challenge to the national railway infrastructure and we’re sorry for the impact they will have on our services on Monday and Tuesday.

“Network Rail is urging customers to only travel if absolutely necessary and anyone who has to travel should expect longer journey times, short-notice cancellations and disruption.

“We are working on a reduced timetable that provides certainty for our customers, but changes are likely to come at relatively short notice, so if you do choose to travel, please check your journey as close to your time of travel as possible.”

If you choose to delay your travel, please note that the original ticket restrictions will still apply. If you are using an Advance Purchase ticket, please travel as close to the original departure time as possible or make use of Book With Confidence.