Thousands of passengers will suffer major disruption this weekend due to no direct services running between London and Scotland while Network Rail carries out engineering work on two major routes simultaneously.
The Government-owned company said a “congested work programme” means it must close sections of both the East Coast and West Coast main lines on Saturday and Sunday.
Watchdog Transport Focus told the PA news agency “this situation should not happen”.
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Journeys between London and Scotland will be significantly slower than usual and require at least one change.
An itinerary suggested by National Rail Enquiries for passengers travelling from London to Edinburgh on Saturday morning involves three trains and one bus.
That journey is expected to take a total of six hours and 12 minutes, nearly two hours longer than the normal direct service.
The West Coast main line runs between London and Glasgow, with branches to Birmingham, North Wales, Liverpool, Manchester and Edinburgh.
It will be closed between Wigan North Western and Lancaster during the next three weekends and Sunday March 12 to enable track upgrades at Preston station.
When there is engineering work on that route a full service usually operates on the East Coast main line, which stretches between London and Edinburgh via locations such as Peterborough, Doncaster, York and Newcastle.
But there are no trains between London and St Neots, Cambridgeshire, this weekend while a new signalling system is brought into use.
Among the operators affected by the closures are Avanti West Coast, LNER and Lumo.
Transport Focus chief executive Anthony Smith said: “Passengers will be disappointed to see both East and West Coast lines closed due to engineering works this coming weekend.
“This situation should not happen.
“One line should be kept open so that passengers from Scotland and the north of England have access to a direct train service to London.
“Both train operators and Network Rail must ensure that there is effective communication to support passengers.”
A Network Rail spokeswoman said: “We always try to have a direct cross-border route open, but that has not been possible on this occasion.
“The industry – both Network Rail and train operators – have looked at the alternatives, all of which cause more disruption for passengers.
“We also have a congested work programme caused by landslips, floods and strikes, severely limiting those alternatives.
“We understand the inconvenience this will cause to some of our customers and wish to reassure them that this will be a one-off.”