The London Kings Cross to Edinburgh sevice via Doncaster is among the routes affected today, amid warnings that the disruption caused could continue for days.
Hitachi 800 trains were pulled from lines yesterday as a ‘precautionary’ measure after the fault was found on some trains.
Robert Nisbet regional director at the Rail Delivery Group, told BBC Breakfast this morning: “With the inspections completed initially by the end of today, we are still expecting some disruption to carry on for a few days.
“It’s impossible for me to say exactly how long that is going to take, but we are obviously going through this as quickly as possible, but we don’t want to rush it.
“We want to ensure that all of those trains are thoroughly inspected and cleared and put into service when things are ready, but there may well be a knock-on effect for some of those timetables into next week.”
He said the cracks – measuring millimetres – are on the ‘lifting points on the underside of the carriages used for maintenance’.
Mr Nisbet said: “It’s fair to say this didn’t pose any particular danger to passengers that were travelling on those trains but if you don’t treat these kind of issues early on then they have the potential to develop.”
Hitachi Rail has apologised for the disruption, after cracks were spotted during routine checks, but it said that by Saturday evening some trains had been cleared to run as normal.
A spokesperson for the firm said: “Safety is our number one priority and as a precaution, the decision was taken to halt the entry into service of our intercity fleets pending inspection.
“We understand the frustration caused and we would like to apologise for the inconvenience caused to passengers and operators.“Having been cleared for service, some trains are now running again across the network.”
Rail minister Chris Heaton-Harris has asked operators to deploy extra staff to help passengers complete their journeys and access refunds.