Rail fares are to increase at the slowest rate for five years, an industry body has announced, but more commuters will be pushed into the £5,000-plus bracket for an annual season ticket.

Ticket prices will rise by 2.2% on average from January, the Rail Delivery Group announced on Friday.

The government said in September that regulated fares, which include season tickets, single walk-up fares and off-peak services on long distance journeys, would be frozen at 2.5%, the same level as the retail price index (RPI) in the summer.

The increase in regulated fares means that more rail travellers will pay more than £5,000 for an annual season ticket from 2 January. Those commuting from Canterbury East to London, for example, will see their season tickets rising from £4,960 to more than £5,000; Folkestone Central to London season tickets, which were £4,984 in January 2014, will also exceed £5,000.

Other travellers will join the ranks of those already paying £4,000 a year for their annual commute. A season ticket from West Malling in Kent to London, for example, will climb from £3,996 at the beginning of this year to more than £4,000.

Though the increase to regulated fares has been capped at 2.5%, the amount added to unregulated fares, such as off-peak leisure tickets, is left to train companies’ discretion.

The Rail Delivery Group said the average rise for all fares to take effect from 2 January would be 2.2%.

“Over the next five years, Network Rail is spending on average £27m a day on a better railway, alongside commitments made by train companies to improve services. That will mean more seats, better stations and improved journeys,” said Michael Roberts, director general of the group, which represents rail operators.

However, many season ticket holders will find the increase to be greater than their annual pay rise.

Passenger groups criticised the government for relying on a “discredited” measure of inflation that has allowed rail fares to rise faster than wages.

“During this parliament, many fares have risen three times faster than wages, affecting all those who rely on trains and putting enormous strain on household budgets,” said Martin Abrams of the Campaign for Better Transport (CBT).

According to the group, many commuters will pay 20-25% more for their season tickets in January than in 2010. Between 2010-15, the cost of an annual ticket from Newcastle to Middlesbrough rose 26% to £2,234; a season ticket from London to Oxford will be £4,788, up 22% on 2010.

The CBT has called on the government to drop the RPI as a basis of fares and use the consumer price index favoured by the Office for National Statistics. The UK’s statistics body announced in 2013 that RPI fell short of international best practice, a view shared by many economists, who argue that RPI is a flawed way of calculating inflation that overstates how quickly prices are rising.

“Whoever is in power after the general election urgently needs to adopt a much fairer approach to ticket prices,” Abrams said. “There must be a permanent end to above-inflation fares rises, not just the temporary respite currently in place.”

Labour and rail unions echoed campaigners’ anger. Manuel Cortes, leader of the TSSA rail union, said it was time to stop “this annual persecution of passengers” with fare rises. “We have seen fares jump by as much as 245% on key routes since privatisation 20 years ago. It is now cheaper for a family of four to fly to Iceland than it is for one person to buy an ‘anytime walk-on’ return rail fare from London to Manchester (£321).”

Mick Cash, general secretary of the RMT union, said: “The scandal of Britain’s great rail fares rip off continues with today’s hike far out stripping average pay increases, and it will once again hit those at the sharp end of the austerity clampdown the hardest.”

Lillian Greenwood, Labour’s shadow rail minister, accused the government of being out of touch. “Passengers on the morning commute know the reality of this government’s incompetence. The collapse of franchising in 2012 cost over £50m, and millions more has been lost through reduced premium payments. That money could have been used to address the cost of living crisis, but now passengers are paying the price instead.”

Passenger Focus, an independent watchdog, said: “Only just over four in 10 passengers are currently happy with the value of their ticket. What is now needed is a more consistent day-to-day service, and a flexible fares structure that delivers the type of products that passengers want.”