First Great Western has apologised to passengers on its Penzance to Paddington train after they were strandded for more than five hours.
Thre company said the train suffered a brake fault leaving hundreds of passengers stranded in a broken-down train for almost six hours when it stopped near Pewsey, Wiltshire.
It said the delay was caused by a fractured air pipe, which forced the brakes to lock. It said refunds would be given.
Passengers described the journey as "horrific" and claimed they were "treated like cattle".
The train was at a standstill for five hours and 40 minutes, arriving at Paddington at about 22:15 BST yesterday.
Passengers complained that the train's onboard cafe ran out of food within the first hour of it breaking down with staff handing out bottled water to children and the elderly.
Others said the train was overcrowded with many unable to sit down during the long wait.
A spokeswoman for First Great Western said: "I'm really sorry for the significant delay experienced by our customers on the 11am train from Penzance to London Paddington. A delay of this magnitude is unacceptable and a full investigation will be carried out."
Engineers were brought in to repair the fault and customers were met at Reading and London Paddington to ensure they were able to complete their journeys following the long delay.
