Trains to and from Euston have been suspended after an overhead cable came down and caused a fire by the side of the track.
Network Rail has urged passengers not to travel unless absolutely necessary after the London-Milton Keynes route was suspended on Tuesday.
This comes after the UK recorded its first ever 40c temperature amid a Met Office red level four extreme warning .
Network Rail posted a picture of the incident, which occurred near Harrow, and confirmed all services to and from London Euston are suspended until further notice
All trains are terminating north of the effected area while London Northwestern Railway also suspended its services south of Northampton.
The cables were mended by electrical engineers as they assess the damage while trees need to cleared from the tracks following the fire.
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.”