Train passengers warned not to travel in heatwave

Trains have been cancelled and railway lines closed as the UK recorded its hottest day on record.

Network Rail issued a "do not travel" warning, with most journeys scrapped through the Met Office's extreme heat zone, which covers much of central, northern, and south-east England.

No services will run into or out of London King's Cross all day.

The cancellations are due to the heat affecting the safety of steel railway tracks, which can buckle when too hot.

Jake Kelly, Network Rail's operations director, said any journey which might go ahead on Tuesday within the Met Office's red zone was going to be "long, disrupted and uncomfortable".

"With free refunds or ticket swaps available, our best advice is to stay home and replan your journey," he added.

Network Rail, which owns and runs most of the train lines in Britain, said there were no Thameslink or Great Northern services planned to run north of London all day.

East Midlands Railway is only running very limited services between Derby, Nottingham, Luton, Bedford and London, which will stop altogether during the hottest part of the day.

The East Coast mainline between the capital, York and Leeds has been shut completely.

Meanwhile, services out of London Euston on Avanti West Coast and West Midlands Railway trains will also be "very limited and disrupted", along with Chiltern Railway trains to and from London Marylebone.

The UK recorded a temperature of more than 40C (104F) for the first time on Tuesday, with the heat expected to climb even higher later.

Transport Secretary Grant Shapps told BBC Breakfast the UK's Victorian-built railway lines "just wasn't built to withstand this type of temperature - and it will be many years before we can replace infrastructure with the kind of infrastructure that could, because the temperatures are so extreme".

Asked if the transport system can cope with the weather, he said: "The simple answer at the moment is no.

"Where those tracks are 40C in the air, on the ground that could be 50, 60, 70 and more, so you get a severe danger of tracks buckling.

"What we can't have is trains running over those and a terrible derailing. We've got to be very cautious and conscious of that, which is why there's reduced speeds on large parts of the network."

Railway speed restrictions have been brought in across most of England and Wales, with reports of buckled tracks and overheard wire systems failing on Monday.

Trains that do run have been mostly be limited to speeds of 90mph, down from 100mph or 125mph, while some had to travel as slow as 20mph.

Speed limits for trains are brought in when temperatures soar as steel railways absorb heat easily and tend to be around 20C (68F) above the surrounding air temperature.

The restrictions help because a train exerts less force when it's going more slowly, meaning the rail is less likely to buckle in the heat.

Overhead power lines - especially less modern ones - can also expand and sag in hot weather, and so travelling slower reduces the risk of damage.

In a bid to try and stop tracks getting too hot, Network Rail paints "hot spot" sections of track white so they absorb less heat.

Kevin Groves, of Network Rail, said railways across the world were designed to operate in a temperature range of 45 degrees, with the scale for steel tracks in the UK engineered between -10 to 35C.

He added operators had "fingers crossed" services would return to normal on Wednesday, but a lot depended on the extent of damage to the railways.