Hundreds of rail passengers were forced to abandon their trains and walk along the tracks near Loughborough Junction in south London on Saturday after services ground to a halt during the year's hottest day.
The incident affected multiple Thameslink services, leaving travellers stranded without power or air conditioning as temperatures soared above 33C.
Social media footage captured the extraordinary scenes of passengers filing along the railway tracks beside stationary trains.
The evacuation came after some travellers had endured up to two hours trapped inside sweltering carriages, prompting angry complaints about the handling of the situation.
Angela Lewis, who was among those affected, posted a video on X showing passengers gathered outside Loughborough Junction, writing: "After nearly two hours on the stuck train to Gatwick we are abandoned outside."
She later added: "Was it entirely necessary to keep us waiting nearly two hours in stuck in an overheated carriage for that? we should have been out within 30 minutes max."
Another frustrated passenger wrote to Thameslink: "You will have hell to pay. We've been stuck on this hot and humid train for over an hour."
Thameslink responded that the train would be "getting evacuated shortly" and asked passengers to wait for response staff to establish a safe evacuation route.
Thameslink acknowledged the severity of the situation, with a spokesperson stating: "Earlier today, a fault on a train near Loughborough Junction brought all services to a halt in the area, three of them outside station platforms."
The company explained that the loss of power and air conditioning on such an exceptionally hot day prompted them to mobilise resources from across Sussex and Kent to facilitate passenger evacuations.
"This would have been a difficult and uncomfortable experience for our passengers and we are truly sorry," the spokesperson added.
Both Govia Thameslink Railway and Network Rail issued apologies for the significant disruption caused to travellers.
The Met Office confirmed that Surrey recorded provisional temperatures exceeding 33C, officially marking Saturday as 2025's hottest day to date.
The extreme heat coincided with a yellow warning for thunderstorms affecting south-east Scotland, Yorkshire, the Midlands and Wales from Saturday evening until 3am Sunday.
Forecasters warned that up to 40mm of rain could fall within two hours, urging residents in affected areas to prepare for potential flash flooding.
An amber heat-health alert, the first issued by the UK Health Security Agency since September 2023, remained in effect across all English regions throughout the weekend.