Network Rail has escaped a fine that could have run into millions of pounds for Christmas engineering work overruns at King’s Cross and Paddington stations - despite rail regulators finding it led to “unacceptable” service levels.

In a report today, the Office of Rail Regulation (ORR) said 115,000 passengers were caught up in “widespread confusion, frustration, disruption, discomfort and anxiety” in the overruns, which affected services on December 27 and 28.

In today’s report the ORR said it did not consider it appropriate to take further action against National Rail (NR) given the company had accepted its recommendations and was doing work to remedy failings - despite it having fined the firm £14million for a similar overrun over Christmas 2007.

“Passengers were really let down,” said ORR’s railway markets and economics director Joanna Whittington.

The overruns led to Paddington being closed for part of the day on December 27 and King’s Cross being closed all day. There were chaotic scenes at Finsbury Park where the crush was so great at one point that passengers were unable to disembark and the station closed due to overcrowding.

In today’s report the ORR said reporting of the progress of works at Paddington was inaccurate, meaning the contingency plan was not kicked into action until too late. The plans at King’s Cross also did not take proper account of the impact of failing to hand back a working line on December 27, said the report.

The ORR made a number of recommendations to ensure “that in future passengers do not suffer the same experience”.

The report said: “Passengers who travel between Christmas and the new year include families with young children, the elderly and vulnerable often travelling with lots of luggage in an unfamiliar environment.

“Over the two days we estimate that more than 115,000 passengers were affected in some way by this disruption.”

The report went on: “There were impressive examples of good service from individual members of staff but the overall service passengers received was not acceptable.

“It led to widespread confusion, frustration, disruption, discomfort and anxiety.”

Ms Whittington said: “While the company generally has a good record for delivering engineering work on time, in this instance passengers were really let down.”

She said inadequate contingency planning “did not fully consider the impact of potential overruns on passengers” and needed to change.

Michael Roberts, director general of the Rail Delivery Group which represents operators and NR, said: “Many passengers did not get the service they deserved in the days following Christmas and for that we are very sorry. NR and operators are working closely together to avoid making the same mistakes again.”

David Sidebottom, director at rail customer watchdog Passenger Focus, said travellers “were left angry and frustrated” at the delays, adding: “We heard of passengers standing for hours on trains, locked outside stations and left to find out what to do by themselves. This cannot happen again.”

Transport secretary Patrick McLoughlin said: “Passengers should be at the heart of everything the rail industry does. The industry must learn lessons to avoid any repeat of the completely unacceptable disruption we saw in December.”