Cameron and Miliband clash over rail fares
Labour leader Ed Miliband has accused the government of failing to protect commuters from being "ripped off" over rail fare rises.
During Prime Minister's Questions, he said the government had reversed safeguards put in place, putting an extra £300 on some season tickets.
But David Cameron said Labour had allowed greater rises when in power.
He added that Mr Miliband was not "prepared to take difficult decisions" on funding railways.
The average rise for all rail tickets this year - including unregulated fares such as advance and business tickets - is 5.9%
But commuters have faced increases of up to 11% on ticket prices, according to the watchdog Passenger Focus.
The two leaders clashed over caps on fare increases in the first PMQs of 2012 - ahead of a Labour-led Commons debate on the issue.
Mr Miliband said the coalition had axed a Labour initiative which stopped some train firms from increasing fares by substantially more than the standard "inflation plus 1%" cap.
The Labour leader said the last government had acted to rein in train operators from January 2010 amid concerns that they were "taking advantage" of a flexibility clause in the fare capping system, which permitted them to increase some regulated fares by 5% over the national cap.
"We took away that power from them," he said. "You came to office and you brought the power back, you made the wrong decision."
Mr Miliband added: "That's why the companies are able to rig the fares. That's why someone travelling from Northampton to London will see a rise in a season ticket of over £300."
He challenged the prime minister to "stand up to the train companies, get a better deal for commuters and change your policy".
Mr Cameron acknowledged Labour had scrapped the flexibility clause in 2010, but said this was a one-off move and Labour had "no intention" of making it permanent.
"Labour introduced the policy of 5% flexibility," he said. "They changed it for one year only - for an election year."
The Department for Transport said a flexibility clause had been in place since 1995 - but that it was increased from 2% to 5% above inflation in 2004.
Mr Cameron argued that Labour's policy while in power had resulted in some passengers seeing annual fare rises of 11%.
Later during the Commons debate, Transport Minister Theresa Villiers said Labour's former transport secretary Lord Adonis had only negotiated a "one-year contracted suspension" with train operators, rather than a permanent change.
But Lord Adonis told the BBC it had been his "firm intention" to continue the policy in subsequent years, had Labour been re-elected.
"I was mystified when Philip Hammond, my successor, reinstated the fares flexibility," he said.
The prime minister defended the government's record on rail investment, saying it was supporting Crossrail, the electrification of the Great Western line and the line between Manchester and Liverpool and had approved a high-speed link, initially to run between London and Birmingham.
"There's only two places money for the railways can come from," he added. "It can come from the taxpayer or it can come from the traveller."
The Association of Train Operating Companies said the average rise in season tickets had been set by the government since 2004.
"When setting fares, train companies are subject to strict rules that have been rigorously implemented by both this government and the last," a spokesman said.
"Within this highly regulated system, operators can vary the price of individual season tickets.
"But regulated fares that go up by more than the average must be balanced by others that rise by less than the average. These changes are weighted, meaning that train companies cannot put all the highest fare rises on the busiest routes."