Passengers are being advised not to travel with all trains suspended between London Euston and Milton Keynes as Britain records its hottest day in history.
The emergency services are dealing with a line side fire caused after 25,000 volt overhead electric cables which power trains came down in Hatch End.
All services to and from London Euston are suspended until further notice.
In the meantime, all trains are terminating north of the affected area at stations such as Milton Keynes and Rugby.
London Northwestern Railway has suspended all of its services south of Northampton.
Specialist Network Rail electrical engineers can assess damage caused to the cables and immediately start the repair once given the all clear by the fire service.
Trees involved in the fire can also then be cleared from the tracks.
James Dean, Network Rail’s West Coast South route director, said: “As predicted the extreme temperatures have impacted the overhead cables on the West Coast main line and all trains have had to be stopped at Harrow in North London.
“Please follow our ‘do not travel’ message today as journeys are being severely impacted. Once the emergency services give us the go ahead we will work as fast as we can to restore the railway lines. We’re sorry to people impacted and we’re working as fast as we can to get things back up and running.”
Avanti West Coast and London Northwestern Railway passengers with tickets dated Monday 18 or Tuesday 19 July who cannot travel are entitled to a full refund via their point of purchase.
Alternatively, their tickets will be valid on Wednesday 20 or Thursday 21 July.
As this incident is ongoing people are being urged to check National Rail Enquiries at www.nationalrail.co.uk for the latest travel information, or to follow Euston station’s Twitter account @NetworkRailEUS.
People are being urged to make their journeys after the heatwave has passed.