The Government has called on a North East train manufacturer to provide a comprehensive plan to resolve rail disruption and prioritise safety.
On Saturday (8 May), cracks were identified on the lifting points under the carriage of some Hitachi Class 800 trains. As a precaution the trains were taken out of service until safety inspections were carried out.
The trains are made at the Hitachi factory in Newton Aycliffe.
Rail Minister Chris Heaton-Harris has requested a comprehensive plan from Hitachi to identify the extent of the cracking and whether carriages can still run safely with them.
He also said he expects Hitachi to set out a comprehensive inspection regime guaranteeing that safety is prioritised.
Removing the trains from service led to cancellations and disruption across the network with LNER and Transpennine warning passengers not to travel.
Hitachi opened its £82 million factory in Newton Aycliffe in 2015 and went into production of the Class 800 series, known as Azuma LNER trains. It is thought 180 trains were undergoing the safety checks.
LNER and Transpennine asked passengers to not travel but said tickets will be valid until May 16.
As safety checks are completed, trains are returning to service but the Department for Transport warned significant disruption is expected throughout next week.
Passengers are being told to check before travelling and ensure they have reservations.