The average cost of regulated rail fares – mainly season tickets and one-day tickets – is set to go up by 3.2% in January.

But the exact fare rises across the Greater Anglia network will not be revealed until September or October.

The overall rise is governed by July’s inflation rate – using the Retail Price Index – which was revealed to be 3.2%. Individual fares are likely to rise at a similar level to that, but could be slightly lower or higher so long as the overall average is no higher than that figure.

Around 40% of fares will rise by this amount in January – it will not affect advance-purchase fares which are not controlled by the government.

It uses the July Retail Price Index (RPI) measure of inflation - announced by the Office for National Statistics on Wednesday - to determine the cap on the annual increase.

A 3.2% increase for season tickets from Ipswich to Liverpool Street would push the cost up by £210 a year, from £6,548 to £6,758. The cost from Colchester to Liverpool Street would go up by £163 a year from £5,104 to £5,267.

A Greater Anglia spokesman said: “Fares levels for season tickets and standard returns are regulated and set by the government of the day, with the July RPI figure used as the basis for the following January’s ticket price changes.

“The fare changes for January 2019 will be finalised and announced towards the end of 2018. This year we have cut or frozen many of our off peak and advance fares.

“We’re investing heavily in improving the reliability of our existing trains, upgrading stations, making ticket purchase simpler and easier, improving car parks and raising customer service standards, to ensure that our customers get the best possible value for money.”

Rail, Maritime and Transport union general secretary Mick Cash said: “With passengers already furious at the shocking level of service on Britain’s rip-off privatised railways, today’s news is just another kick in the teeth that will come back to haunt both the Tory government and the train companies alike.”

Transport secretary Chris Grayling has said he is looking for future rises to be based on the Consumer Price Index for July – which was 2.5% this year – but that prompted anger from the RMT who fear it will lead to a cap in their members’ pay rises.