Commuters are enduring chaos and disruption on the railways as the UK swelters on its hottest July day on record amid fears tracks could buckle.
A reduced timetable in the South East came into force at midday as Network Rail implemented speed restrictions, pointing out that steel rails expand under pressure from trains.
Tracks are less likely to buckle if trains run more slowly, it said. Speed limits on most commuter lines have been reduced from 60mph to 30mph.
It warned that disruption is likely to continue into Friday morning.
But the extreme conditions also caused damage to overhead electric wires, blocking all lines between London and Luton.
Overhead wire failures also caused disruption between London and Watford, between Preston and Carlisle and in the Birmingham area.
Many operators have urged passengers not to travel as services are delayed and cancelled.
In one incident, passengers were stranded on a Virgin train without an any air conditioning outside London Euston today and had to be rescued to by rail workers.
Network Rail’s network services director Nick King said: “We have a number of heat-related incidents across the rail network this evening that are causing disruption to services.
“We are sorry that some passengers are experiencing uncomfortable conditions and inconvenience.
“Our teams are working flat-out to fix the issues as quickly as possible and get people on the move.
“We’re asking anyone travelling this evening to check with their train operators or visit the National Rail Enquiries website to see how their journey is affected.”
Further travel disruption could be caused by thundery downpours prompted by the sweltering temperatures, with flash flooding and even power cuts possible.
The Met Office said a new record temperature for the month was set at 38.1C in Cambridge on Thursday afternoon, beating the previous record of 36.7C set in Heathrow in 2015.
It is also the second hottest UK day on record, beating the 37.1C recorded in August 1990.
The Met Office said the current record for the highest overnight temperature in the UK is 23.9C, set in August 1990.
On Wednesday night some places experienced a “tropical night” with temperatures staying above 20C, and that is likely to be repeated on Thursday into Friday.