Hard-hit rail commuters face a greater-than-expected 6.2 per cent hike in average fares in the new year after official figures revealed a shock rise 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 in 2013, rose to 3.2 per cent from 2.8 per cent the previous month, according to the Office for National Statistics.

The City had expected the rate to remain flat at 2.8 per cent.

The average fare increase for England is calculated by adding three per cent to RPI, meaning a hike of 6.2 per cent, although some tickets can go up by a further five percentage points - or more than 11 per cent - as long as they are balanced by cuts on other fares.

Meanwhile, protests are taking at train stations in London today over the fare rises.

Unions, transport campaigners and rail passenger groups have launched a day of action to protest at the possible "massive" fare increases and cuts to jobs and services.

A series of demonstrations are being held at more than 40 railway stations including Waterloo, Euston and Kings Cross.

Bob Crow, leader of the Rail Maritime and Transport union, said passengers will be "rightly angry" when they find out the full extent of inflation-busting fare increases imposed on them by government "diktat".

It is also feared up to 20,000 jobs are at risk under cost-cutting proposals, which will hit station staff, guards, catering and ticket offices.

Stephen Joseph, chief executive of the Campaign for Better Transport, said: "The government knows they can't continue to hit commuters - that's why they've postponed the fuel duty increase. Now they need to give the same help to rail users."

TUC deputy general secretary Frances O'Grady said: "The government is asking train operators to make cuts to staff on trains, stations and in ticket offices while continuing to receive public subsidy and give millions in dividends to shareholders."

Mr Crow said: "The case for renationalising our railways, and throwing the extortionists and rip-off merchants off the tracks, is now overwhelming. 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."

Transport secretary Justine Greening said: "I am keen to see what we can do to keep rail fares down to something affordable. I shall be looking at whether there is a way of doing that in the autumn but we have to stick with our deficit-reduction policy."

Michael Roberts, chief executive of the Association of Train Operating Companies, said: "The government decides the average increase of commuter ticket prices and other regulated fares which train companies will be required to introduce in January 2013.

“It has been government policy during the past eight years for passengers to pay a larger share of the cost of operating the railways and to focus taxpayers' money on investing in longer term improvements to the network. Any flexibility train companies have within the rules is to maximise revenue for the government."