Rail commuters will be hit with weeks of disruption because of hairline cracks found in the undercarriages of high-speed trains.
Dozens of the Hitachi 800 Class trains remained off the tracks for a third day as inspectors carried out safety checks, leading to huge reduction in customer services.
Today Great Western Railway customers on the mainline were told 'not to travel' as there is 'no service or an extremely limited service' between London Paddington and Bristol Temple Meads, Swansea, Penzance, Hereford and Cheltenham Spa.
London North Eastern Railway (LNER) has also had to reduce its service on the East Coast Main Line, which runs between London King's Cross and Edinburgh via Peterborough, York and Newcastle.
But with questions over how long the disruption would last, the operator posted a message on Twitter stating the issue is 'likely to be going on for a number of weeks'.
The cracks in the trains' yaw dampers, the area where the suspension system attaches to the body, that led to the disruption were detected on May 8 during an inspection of a train at GWR's Stoke Gifford depot near Bristol.
Rail commuters will be hit with weeks of disruption because of hairline cracks found in the undercarriages of high-speed trains. The cracks were discovered during tests early on Saturday on the chassis area of some Hitachi Class 800 series trains (stock photo)
The cracks in the trains' yaw dampers, the area where the suspension system attaches to the body, that led to the disruption were detected on May 8 during an inspection of a train at GWR's Stoke Gifford depot near Bristol
However, the inspection had been prompted by the withdrawal of eight Hitachi 800s from service on April 28 when similar hairline cracks were found.
Hitachi confirmed to Rail Business UK that four of the six units stopped for inspection since been passed as 'all clear' and returned to service, while the two initially found with cracks were being repaired.
While a root cause has not yet been identified, initial reports suggested that the problem may be 'fatigue related'.
It comes weeks after a number of CAF trains operated by Northern Rail were taken out of service after the failure of a yaw damper mounting bracket.
Frustrated customers shared their woes on social media with some desperately seeking answers from operators about how to get across the country.
Charlie Hammans, a forest preservation worker tweeted: 'Hi all. Urgent hospital appointment tomorrow in London and stranded in Exeter. Can anyone help with a lift?'
Great Western Railway, which runs trains to South West England and South Wales, and London North Eastern Railways, which serves the East Midlands, the North and Scotland, were worst affected [File photo]
Fintan O'Regan asked GWR how he would be able to make the unenviable journey back to London from Penzance, 280 miles away, without the usual four-hour direct route.
'LNER had better fix these cracks in their trains before I travel,' commented Susan McLellan, adding: 'Engineering works have already cut my trip short by a day.'
Teacher Ben Fuller took a more light-hearted view, saying that while operators were checking the trains for safety 'perhaps they could take a bit longer and fit seats which are actually comfortable?'
A spokesman for the Rail Delivery Group said the operators were publishing the latest train timetable information on their websites.
Rail minister Chris Heaton-Harris described the ongoing disruption was 'disappointing' as passengers had started to return to using the train network following coronavirus restrictions.
Frustrated customers shared their woes on social media with some desperately seeking answers from operators about how to get across the country
Asked how long the trains had been running with the cracks, he told BBC Radio 4's Today programme: 'These trains are relatively new in service, so this is something that the Hitachi engineers will be looking at and reporting back to the train operating companies.
'For us, as an industry, it's disappointing and it's dispiriting in a way to have this happen, because we were just starting to see passengers come back onto the network after a very difficult pandemic for the whole transport sector.'
The Department for Transport said Mr Heaton-Harris had called an urgent meeting with MPs on Sunday to keep them updated on progress, with representatives from Hitachi and the train operators also invited.
Robert Nisbet, regional director at the Railway Delivery Group, said that if the trains being inspected were found to have 'tiny cracks', they would need to be treated and replacement trains brought in.
Asked if he knew how long the disruption was likely to last, he told BBC Radio 4's Today programme: 'No, I can't put an exact time on it and that is purely because we are going through the process and taking it extremely seriously.
Several London North Eastern Railway (LNER) trains were seen arriving for checks in the service halls at Bounds Green Service Depot, which used by Hitachi
The new cracks, measuring millimetres deep, are understood to be on the mechanism used to jack up carriages when they are being fixed
Not the first time commuters have had trouble with Hitachi 800 trains
Hailed as the 'smartest trains in the country' by then Transport Secretary Chris Grayling, the long-awaited Intercity Express was meant to mark a new era of train travel across the country.
However, its maiden voyage in 2017 saw a throwback to the age-old complaints - delays, no available seats, broken aircon and tickets costing £200.
The first Hitachi 800 was due to leave Bristol Temple Meads for London Paddington at 6am but didn't depart until 6.25am for unspecified 'technical issues' - and arrived 41 minutes late.
Passengers were still forced to stand, despite claims that capacity on the new trains was increased by 20 per cent, and one had their laptop damaged as water from the air conditioning poured into one of the carriages.
There was further embarrassment when the maiden journey ground to a halt at Taplow, Buckinghamshire, all while Transport Secretary Chris Grayling was on board.
The IETs eventually became faster, but ran at the same 1 hour 45 mins journey time from Bristol to London for a whole year while work to electrify the whole route took place.
'If some of these trains that are being inspected for these tiny cracks are found to have them, then obviously those cracks need to be treated, in which case replacement trains may need to be brought in to fill those places on the timetable.'
A total of 182 were taken out of service that day with a number returned to the network by yesterday after being given the all-clear.
Industry sources said it could last until at least the end of the week. Safety watchdog the Office of Rail and Road is overseeing the process.
Engineers were checking carriages at depots near London and Bristol over the weekend.
GWR, who are worst affected, had previously detected hairline cracks underneath a handful of Hitachi trains in late April.
It is thought this led to further cracks being discovered elsewhere, leading to the 182-strong fleet of Hitachi 800s being taken out of service.
The new cracks, measuring millimetres deep, are understood to be on the mechanism used to jack up carriages when they are being fixed.
It is not believed they pose an immediate danger.
Hitachi trains have speeds of 125mph and came into service in 2017.
Hitachi Rail apologised on Saturday for the disruption after the cracks were spotted during routine checks, adding that by Saturday evening 'some trains' had been cleared to run as normal.
A spokesperson 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.'
RMT rail union General Secretary Mick Lynch said: 'RMT is fully aware of the issues that have led to the cancellation of services on LNER today and that similar problems with cracks appearing in the fleet on Great Western are also emerging.
'Hitachi needs to ensure the highest safety standards and properly investigate and rectify the issues.
'This situation demonstrates once again that it is reckless for the rail companies and the DfT to move the industry to diluted, risk-based maintenance regimes which extends maintenance cycles on rolling stock or on the infrastructure, whether that be on the mainline railway or on the tube and metro services, to cut costs and strip out staff.
'The railway needs to be maintained rigorously and to the highest possible standards to protect the travelling public and the staff and that will remain RMT's key demand.'