Rail delays which disrupted thousands of journeys at the New Year have been criticised as a "fiasco", by MPs.
Engineering work at Rugby caused delays for thousands
For the Tories Theresa Villiers blamed "incompetent" Network Rail managers and said ministers had not set up an effective system to penalise failures.
Delayed engineering work on the West Coast Mainline at Rugby and at London's Liverpool Street caused days of delays.
Transport Secretary Ruth Kelly said the delays were "unacceptable" but were being investigated and lessons learnt.
The Office of Rail Regulation began the inquiry after West Coast Mainline work overran by four days - at Liverpool Street bridge work also overran.
Network Rail has apologised and said the delays were unacceptable and caused by a shortage of specialist engineering staff.
But in a Conservative-led Commons debate on Network Rail, Shadow transport secretary Ms Villiers said a "monumental foul up" had led to a "truly miserable New Year greeting from this government and Network Rail".
"It is simply not acceptable, it should not have happened. With sensible planning it need not have happened."
She said Labour had created Network Rail to oversee work on the railways, but it was "not properly accountable to anyone" adding: "When it provides poor service, too often it gets away with impunity".
For the Lib Dems, Norman Baker told MPs the episode had been a "fiasco" and better planning was needed so the railways could be relied upon every day of the week.
"The public at large and indeed the freight operators are entitled to a railway that is safe, clean, that is fairly priced, cost efficient and is predictable in terms of when it's going to run and when it's going to arrive and its projected destination," he said.
For the government, Ms Kelly said the problems at the New Year had been "serious and unacceptable" but were being investigated by the ORR.
She said Network Rail's chief executive had told her he intended to "learn all the lessons" to minimise the risk of future delays.
But she said Labour had taken "tough decisions required to clear up the mess left after privatisation where the state of the track had deteriorated dramatically" and while the previous Tory government had "managed decline", Labour was "planning for growth".
"We are not complacent, it's clear that recent events show that Network Rail has a lot more work to do," she said.
She said once reports from the ORR and Network Rail were in, she would be able to see "what, if any, steps need to be taken and prevent a recurrence".
A Conservative motion calling the delays "unacceptable" and calling for Network Rail to be made more accountable to the travelling public was defeated by 303 votes to 235 - a government majority of 68.
A government amendment praising its "decisive action to correct the flaws of rail privatisation" was carried by 304 to 234.