The disruption to rail traffic caused by the discovery of cracks in some trains could last for days, according to the Rail Delivery Group.
Hitachi 800 trains were pulled off lines on Saturday as a “precautionary measure” after the fault was discovered on some trains, and the Great Western Railway (GWR) and London North Eastern Railway (LNER) advised people on Sunday not to drive.
Robert Nisbet, the panel’s regional director, told BBC Breakfast: “Having originally completed the inspections by the end of today, we still expect some disruptions to continue for a few days.
“It’s impossible for me to say exactly how long this will take, but we’re obviously going through this as soon as possible, but we don’t want to rush it.”
“We want to make sure that all of these trains are thoroughly inspected and cleared and put into service when things are done, but there may well be an impact on some of these schedules over the next week.”
He said the millimeter-sized cracks were on the “lifting points on the underside of the car used for maintenance.”
Mr Nisbet said, “It is fair to say that this did not pose a particular threat to passengers traveling on these trains, but if you do not address these types of issues early on, they have the potential to develop.”
Hitachi Rail apologized for the disruption on Saturday after the cracks were discovered during routine checks, adding that “some trains” had been cleared for normal operation by Saturday evening.
A spokesman said: “Safety is our top priority. As a precaution, it was decided to stop the commissioning of our intercity fleets until the inspection.
“We understand the frustration and apologize for the inconvenience caused to passengers and operators.
“After some trains have been released for service, they are now back on the network.”
Rail Minister Chris Heaton-Harris has asked operators to deploy additional staff to help passengers make their journeys and access reimbursements.
He added, “I share the frustration of passengers experiencing significant disruption and would ask people whose journeys are affected to check before traveling.”
The non-ministerial government department responsible for regulating UK railways, the Office of Rail and Road (ORR), said it has opened an investigation to “gather the full facts of the problem and all the lessons that need to be drawn”.