Commuters faced serious rush-hour disruption after rail services to and from London were hit by damage to overhead wires.
Issues at Stevenage and Hayes & Harlington are causing severe problems for services through London Kings Cross, Paddington and Moorgate.
Those travelling towards points north and south of the capital, including destinations in the far north and Scotland as well as central and southern England, are having to cope with cancellations and severe delays due to the damage at Stevenage.
Affected passengers are being warned that services will remain disrupted for the rest of the day.
Meanwhile, the further damage to overhead wires at Hayes & Harlington means fewer services are able to run from Paddington station to destinations in the west, including destinations in Wales, and south-west England, as well as Heathrow Airport.
The problem in the area arose at around 6:30am on Monday after a number of trains became entangled, the PA news agency understands.
All four lines serving Paddington reopened on Tuesday morning after a 27-hour suspension, but the wires were only working above two of them.
The station will close again at 10pm to allow engineers to complete the repairs.
Engineers will work overnight, meaning no GWR and Heathrow Express services will run in and out of London Paddington until 6am on Wednesday.
National Rail is advising passengers to use alternative routes to reach their destinations.
The damage at Hayes & Harlington meant a day of mayhem for mourners who travelled to London for the Queen’s funeral.
The problem caused thousands of mourners to miss the funeral service or to resort to watching it on phones in carriages and on platforms.