The Office of the Rail Regulator is to look into the severe disruption caused by overrunning engineering work to London travel services.
King's Cross station was shut and passengers instructed to use Finsbury Park instead. However, there were "chaotic scenes" at Finsbury Park, according to the BBC, with long queues of people trying to enter the station. The station was closed for an hour at 11am due to overcrowding.
There are no services between London Paddington and Reading due to engineering work.
Passengers were advised to use alternative routes by First Great Western and Chiltern Trains. The companies have also offered refunds to commuters on tickets.
West Coast Main Line services are also not running between London Euston and Hemel Hempstead in Hertfordshire until 29 December, also due to engineering works.
A spokesman for the rail regulator said: "The immediate priority is for Network Rail to ensure disrupted parts of the railways are back up and running again for passengers as soon as possible.
"Network Rail, working with the rest of the industry, must learn lessons and prevent problems like this happening again."
Network Rail said the work near King's Cross was part of a £200m Christmas investment programme and described the move to cancel all services as "regrettable and unfortunate".
The rail operator, east Coast Trains, apologised for the disruption and said tickets would be valid on Sunday services.
Its spokesperson said: "Passengers travelling to and from London King's Cross are advised to travel on another day if at all possible."
Transport Secretary Patrick McLoughlin is demanding an explanation from Network Rail as to why the disruption has taken place.
McLoughlin will expect "a full understanding" from Network Rail of what went wrong and what can be done to make sure it does not happen again, said a source.
Anthony Smith, chief executive of Passenger Focus, told Sky News: "It's deeply frustrating and annoying for passengers.
"Doing works at Christmas in this filthy weather, things can go wrong - I think passengers understand that. The acid test is how are the delays dealt with - are there plenty of staff out there, is the information good?"
A Department for Transport spokesperson said: "It is extremely disappointing that Network Rail's engineering works have overrun and will affect travellers during this festive season. Passengers will be rightly annoyed.
"This was essential work but passengers need to be able to plan and rely on Network Rail meeting its deadlines for having the network back in service."
Previous investigations by the Office of the Rail Regulator have led to multi-million pound fines.
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Long line of weary travellers at Finsbury Park.