A busy railway line through London, the East of England and the East Midlands is set to shut completely due to a searing heatwave.

Thameslink, Great Northern and LNER are set to cancel all trains out of London King's Cross tomorrow (Tuesday, July 19).

This is because Network Rail is going to close part of the East Coast Main Line between 12pm and 8pm due to potential faults to railway tracks and equipment.

The decision to close the line - which runs through Stevenage, Peterborough, Grantham and York - follows a Met Office red weather warning for "extreme heat", with temperatures set to exceed 38C in the East of England.

%image(14510317, type="article-full", alt="Motorists and railway passengers are being urged not to travel unless essential during a Met Office red weather warning for "extreme heat"")

%image(14510319, type="article-full", alt="Extreme heat can cause rails to expand, meaning they can bend and buckle, a Network Rail spokesperson said")

Sam MacDougall, Network Rail operations director, said: "Closing the line to traffic is always a last resort but it is the right thing to do to keep people safe on Tuesday given the unprecedented heatwave forecast.

"The forecast temperatures are well above those which our infrastructure is designed, and safety must come first.

"The best way to keep everyone safe and prevent passengers from becoming stranded on trains in the extraordinary heat is to proactively close the East Coast Main Line routes south of York and Leeds during the very hottest temperatures.

"I am sorry for the disruption this will cause."

Passengers travelling with LNER will be unable to travel out of London King's Cross on Tuesday, but the firm said tickets can be used on Wednesday, July 20 or Thursday, July 21, with a full refund on offer if customers decide not to travel.

An LNER spokesperson said: "On Tuesday, July 19, do not travel on routes south of York and south of Leeds to London King’s Cross as no trains will run.

"This includes to or from Wakefield Westgate, Doncaster, Retford, Lincoln, Newark Northgate, Grantham, Peterborough and Stevenage."

Thameslink and Great Northern are not set to run any trains between Cambridge and London, with no services through Royston, Stevenage, Welwyn Garden City or Hertford North on Tuesday.

Services into Peterborough, via Huntingdon, and into London Moorgate will also be suspended.

Great Northern is only set to run a shuttle between Cambridge and King's Lynn, via Ely and Littleport.

A company spokesperson said delays and disruption is expected on the remainder of the Thameslink network.

They said: "Only travel if your journey is absolutely necessary."

%image(14510321, type="article-full", alt="Great Northern will run a shuttle service between Cambridge and King's Lynn, via Ely and Littleport")

%image(14510322, type="article-full", alt="Greater Anglia will not run trains between Ely and Peterborough (pictured) for part of the day on Tuesday, July 19")

Greater Anglia trains will continue to run trains throughout its network with a "reduced service" on some lines.

The Ipswich to Peterborough service will terminate and start at Ely between 12pm and 8pm on Tuesday. There will be no trains through March or Whittlesey during the closure period.

A Greater Anglia spokesperson said: "Many journeys are expected to take longer, as trains will be travelling at slower speeds than usual, and service alterations will take place on many routes.

"Passengers are warned to expect widespread disruption and short-notice cancellations, especially from the middle of the day onwards when the hottest temperatures occur."

%image(14510323, type="article-full", alt="The Greater Anglia network has already been affected by "extreme heat" during a field fire in Essex on Sunday, July 17")

Other rail firms, including CrossCountry and Hull Trains, have warned passengers that trains could be cancelled at short notice.