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Ministers have asked Network Rail (NR) to explain how train passengers, including those in Essex, were left "stranded in very uncomfortable conditions'' in ultra-high temperatures.
A series of incidents on mainline services led to delays and cancellations on Monday night and again on Tuesday morning as temperatures touched 32C (90F).
Rail Minister Norman Baker said he was asking NR for an explanation.
But NR said a number of incidents had nothing to do with the hot weather and it was not correct to say that the infrastructure could not cope with a heatwave.
Among the passengers whose services were disrupted were those on National Express East Anglia trains, where there were overhead wire problems.
Mr Baker said: "It is worrying that a significant amount of rail services were disrupted yesterday due to the hot weather, leaving passengers stranded in very uncomfortable conditions.
"We need the railway to be resilient, especially with the possibility of climate change causing more extremes of temperature in the future. I am asking Network Rail to explain to me what happened yesterday and what steps they are taking to try to prevent a recurrence.''
An NR spokesman said: "There has been an assumption that everything that has gone wrong was due to the heat. But we had incidents that were nothing to do with the heat, such as broken-down trains and trespassing on the line.'' He went on: "It's not right to say the infrastructure can't cope with the heat.''
Bob Crow, general secretary of the RMT transport union, said: "Once again this issue of investment in the failing infrastructure of the UK transport system is thrown into the spotlight and the sooner we drop the idea of the railways being run as a money-making racket rather than a public service the better.
"If the money ripped off by the train operators had been invested where it matters we wouldn't be reduced to this sort of chaos as soon as the weather warms up.''