Poor planning, equipment failures and communication breakdowns all contributed to the Christmas rail engineering overruns which led to chaotic scenes at three London stations, a Network Rail (NR) report has said.
Physical work near Paddington station was completed on time but safety validation work that should have taken two hours took 10 hours, the report said.
When work near King's Cross overran the trains were switched to start and finish at Finsbury Park station but "not enough was done" to manage passenger flow at Finsbury Park which had to close for a time, so great was the crush.
Work should have been completed to enable King's Cross and Paddington to open on Saturday December 27. But King's Cross had to stay shut all day and Paddington only opened in the early afternoon.
NR chief executive Mark Carne said today: "A number of things went wrong in these two instances. In addition it is clear that our project back-up plans and the train service plans should have done a much better job in protecting the travelling public from our engineering problems.
"Over Christmas, we undertook the biggest programme of engineering and investment work ever, on train lines across the country. Ninety-nine per cent went to plan but in the case of King's Cross and Paddington we let passengers down.
"I sincerely apologise for the disruption over the festive period and we are determined to learn the lessons so that we can continue to make the improvements the travelling public deserve."
Anthony Smith, chief executive of the rail customer watchdog Passenger Focus, said: "On the basis of this report and the events on the day the industry has a long way to go to restore trust in how it handles these events
"There was no reliable Plan B at King's Cross, so Finsbury Park was pressed into action. At Paddington confusion reigned. Overall few staff were around, information was patchy at best and no-one seemed in overall control. Passengers and government are pouring billions into the railways - they deserve better than this."