Rail services on Great Western Railway (GWR) and London North Eastern Railway (LNER) are being disrupted for a third day due to cracks in trains.
GWR advised passengers with tickets for long-distance journeys "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.
LNER is running a reduced service on the East Coast Main Line, which runs between London King’s Cross and Edinburgh via Peterborough, York and Newcastle.
The rail minister has asked the industry to urgently set out a plan for resuming normal service after some trains had to be withdrawn over the weekend.
Cracks were discovered on some trains on Saturday, resulting in the Class 800 Series made by Japan’s Hitachi being pulled off lines for safety checks.
Hitachi has apologised and said the trains were withdrawn as a precaution.
A spokesperson said: "Inspection has identified cracks on the lifting points under the carriage of some Class 800 trains. Safety is our number one priority and as a precaution this continues to impact the number of trains that can run in service.
"We acknowledge the government’s clear direction regarding the forward repair plan, and our teams continue to work day and night with the ORR, operators and independent experts.
"We thank passengers for their ongoing patience."
LNER promised to rebook or refund tickets for passengers who were affected. Passengers can check changes to the week’s timetable here.
A spokesperson said: "Due to a number of Hitachi Class 800 trains from several train companies being taken out of service for ongoing checks as a precautionary measure, there will be some cancellations across the LNER route from Monday 10 May 2021.
"The issue is being investigated and once trains have been checked, we are reintroducing them back into service as soon as possible.
"We apologise for the disruption caused and are advising customers to check before they travel with LNER from Monday 10 May. "
"The problem continues to be investigated by Hitachi and once trains have been checked and cleared, we hope to be able to release them back into service as soon as possible," said GWR, which is owned by FirstGroup.
Train operators and representatives from Hitachi were invited to an urgent meeting with MPs on Sunday to discuss the problems.
Chris Heaton-Harris, transport minister, said: "Today I have directed the rail industry to urgently set out a comprehensive plan to ensure services can safely resume as soon as possible.
"I expect operators to explore all options for replacement services to help people complete their journeys, and have asked Hitachi for a safety inspection plan, as well as longer term repair strategy.
"Our focus is to ensure trains are returned to service as quickly as possible, once they are fully approved as safe. Only then can we start to rebuild a reliable and punctual timetable for passengers.
"I also want to thank passengers for their patience during what could be a significant period of prolonged disruption, likely to continue for some time."
Mr Heaton-Harris said that train operators should arrange replacement bus and coach services to help their customers.