Rail travellers in England face a greater-than-expected 6.2% hike in average fares from the New Year after official figures revealed a surprise jump in the inflation rate.
The retail prices index (RPI) figure for July , which is used to determine how much regulated rail fares, including season and saver tickets, are allowed to increase from January next year, rose to 3.2% from 2.8% the previous month.
The City had expected the rate to remain flat at 2.8%.
The average fare increase for England is calculated by adding 3% to RPI, meaning an increase of 6.2%, although some tickets can go up by a further five percentage points - or more than 11% - as long as they are balanced by cuts on other fares.
Fares in Scotland will go up by just 1% plus RPI and Wales is yet to set its rise.
Unions and campaign groups reacted angrily to the rise in travel costs and called on Westminster to change its policy on how rail fares are calculated.
Bob Crow, leader of the Rail Maritime and Transport union , said: "This represents a massive blow to the travelling public as they see fares rocket by over 6% in January at a time when household budgets are hit by the Government's austerity programmes.
"People will be rightly angry as they work out what this inflation-busting increase in fares means for them.
"This money will not be invested back in services, it will be trousered by the greedy train operators as another windfall profit."
According to passenger groups, commuters to London routinely spend 15% of their salary on getting to work.
Stephen Joseph, of the Campaign for Better Transport , said that "pressure on the Government to reverse its policy, and bring fares down" was growing.
But ministers insisted the increase was needed to fund modernisation of the rail network.
Rail minister Theresa Villiers told Sky News: "Obviously where we can we take action to relieve pressure on family budgets but there is a limit to what we can do given we inherited a huge deficit.
"But passengers are already seeing the benefits of the railway expansion service."
Transport secretary Justine Greening added that the Government was "keen to see what we can do to keep rail fares down to something affordable."
Michael Roberts, chief executive of the Association of Train Operating Companies, called for train companies to have more freedom from the Government.
He told Sky News that the "secret" to bringing down the costs of the railways was to make them more efficient by reforming Network Rail, which operates Britain's rail infrastructure, and giving companies more freedom from Government restrictions.
Unions also warned that up to 20,000 jobs in the rail industry are at risk under cost-cutting proposals, which will hit station staff, guards, catering and ticket offices.
A series of demonstrations are being held at 40 railway stations across the country today to step up demands for railways to be returned to public ownership.
Campaigners claim that privatisation has led to some of the highest fares in Europe despite a massive increase in taxpayer subsidies to the industry.
Mr Crow called for Britain's railways to be re-nationalised.
He said: "The public is sick and tired of being charged through the nose to travel on creaking, overcrowded trains while the rail companies are robbing them blind."
The Government's railway reforms aim to deliver £3.5bn in efficiency savings while continuing to expand services.