TRAINS running on some of Scotland's key rail routes have had a speed limit of 20mph implement as an amber warning over extreme heat came into force across parts of Scotland.

Network Rail confirmed train speeds would be restricted between 1pm and 8pm on Monday, which will have an impact on at least 13 key ScotRail routes. It has been painting its rails as part of its bid to keep the trains running.

The 20mph speed limit will be in place until tomorrow evening (Tuesday July 19) and travellers were warned to be prepared for delays.

Network Rail Scotland said that the restrictions will impact most train routes during the warmest part of the day, "helping to minimise potential damage caused by today's forecasted temperatures"

Cross border operators have also been altering timetables due to the significantly higher temperatures south of the border and passengers were advised to check their journey with their operator in advance.

Avanti West Coast, which operates between Euston and Scotland, via the West Midlands, has suspended ticket sales for the rest of the day and tomorrow.

The East Coast Main Line which connects London and Scotland will be closed between King's Cross and York and Leeds on Tuesday afternoon.

It comes after the Met Office issued an amber weather warning for Monday and Tuesday in eastern, southern and central parts of Scotland, with warnings that Scotland's highest recorded temperature of 32.9C could be topped this week.

The amber warning from the Met Office is expected to last until midnight on Tuesday.

Restrictions will be in place on an array of routes with delays of between ten and 20 minutes according to ScotRail.

ScotRail affected are between Glasgow Queen Street and Dundee, Inverness, Alloa, Oban, Fort William and Aberdeen. Also hit are journeys between Glasgow Central and Edinburgh via Shotts and Carlisle via Dundee.

HeraldScotland: ScotRail train

Services between Edinburgh and North Berwick, Aberdeen, Helensburgh via Airdrie, Dundee and Milngavie are also affected.

The train operator urged passengers to "plan ahead", tweeting: "Please please please, plan ahead if you're out, it's going to be extremely hot later today. Take water with you, wear sensible clothing - hats/sunglasses, if you've got elderly neighbors/relatives, check up on them."

Network Rail has explained that during heatwaves rails in direct sunshine can be as much as 20°C hotter than air temperature and expand as they get warmer – sometimes causing them to curve or buckle. Metal overhead power lines can also expand in extremely hot conditions.

Network Rail engineers have been carruing out additional track inspections to check for heat-related problems while at some locations special remote monitoring equipment has been deployed to help spot rails which are becoming too hot.

Engineers have been stressing sections of track, a method of artificially stretching the rails, in known hot-spot areas to help them cope with sudden rises in temperature and painting rails white at key locations to help reflect the sun and keep them up to 10°C cooler.

Meteorologist Jim Dale told BBC Radio Scotland's Good Morning Scotland programme that no repeats of the high temperatures are expected over the next few weeks.

He said: "This event is quite unusual. Last time the records were broken it was in a single day and it was just a spike here and there.

"Because we live, particularly in Scotland, in a temperate zone, what we're not talking about is continuous, extreme heat that's going to go on and on and on.

"These are always going to be spikes. I can't see anything at the moment on the charts that suggest, certainly for Scotland, and even down into the London area, that suggest any repeats of this in the next couple of weeks."

A national emergency has been declared in the UK, with an unprecedented red extreme heat warning issued in England.

While Scotland will be cooler, people have been warned to watch out for sunburn or heat exhaustion and the possible risk of power cuts due to failures in heat-sensitive systems and equipment. There is also an increased threat of wildfires due to the intense heat and parched conditions.

The Scottish Government’s resilience minister Keith Brown said: “We are aware of the extension to the weather warnings currently in place and are receiving regular updates from partners including the Met Office and emergency services.

“Our resilience arrangements have been activated and stand ready at all times to co-ordinate a response to severe weather issues where required. We will continue to closely monitor developments.

“When temperatures increase, it’s important to monitor forecasts and follow public health advice, including staying hydrated and drinking plenty of fluids and avoiding excess alcohol.

“I would also urge people to look out for vulnerable family, friends and neighbours, as older people, those with underlying conditions and those living alone may struggle to keep cool and hydrated.”

Meanwhile, Nicola Sturgeon told people to "follow sensible advice" as temperatures soar.

The First Minister tweeted: "The next couple of days are set to be exceptionally hot. Please take care and follow sensible advice - keep out of direct sun; stay well hydrated; and look out for others who may be suffering from the heat."