SPEED restrictions will be in force on South Western Railway services today and tomorrow with people urged only to travel if absolutely necessary.

Temperatures are set to reach up to 40C in London and around the mid-30s in the south west but rail temperatures can be up to 20C higher than the air around them.

Network Rail will introduce speed restrictions across the network in a bid to minimise the force on the tracks and reduce the chance of buckling.

Read more: "National emergency": red heat-health alert issued over heatwave

As a result, the speed restrictions will make journeys longer and South Western Railway will introduce a reduced service on Monday and Tuesday with services to Bournemouth due to be affected.

South Western Railway said service changes are likely to appear in journey planners at short notice with passengers urged to check their journey before setting off and to expect last minute delays and cancellations.

Read more: Heatwave: what you need to know if you live in Dorset

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

South Western Railway'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."

South Western Railway is allowing people with tickets for travel on its services on Monday and Tuesday to travel on Wednesday and Thursday instead.