Prime minister will announce consumer-friendly move – which could save 250,000 season-ticket holders an average of £400 – on Friday

More than 250,000 annual rail season-ticket holders could save an average of £400 over the next five years after David Cameron pledged that the Tories would freeze regulated fares in real terms.

In a consumer-friendly announcement designed to boost Tory fortunes amid flagging poll ratings, the prime minister will say on Friday that regulated rail fares would only be able to rise in line with the retail price index (RPI).

The prime minister will also seek to revive his 2010 election “big society” campaign theme by offering workers employed by companies with a staff of at least 250 people the right to three days of paid leave to volunteer.



“This is the clearest demonstration of the big society in action – and I’m proud it’s a Conservative government that will deliver it,” Cameron said in an echo of the language he used during the 2010 election campaign.

The announcement marked a noticeable shift in gear by the Tories after a day that was dominated by a highly personal attack on Ed Miliband by the defence secretary, Michael Fallon.

In a move to win over vocal rail commuters, who regularly complain about rising fares, the prime minister announced that a two-year, real-terms freeze in regulated fares would be maintained throughout the next parliament. The average commuter would save about £400 over the next five years, on top of the £75 saved by the average consumer during the freeze over the past two years.

Boris Johnson will also announce that he will guarantee a real-terms freeze of all Transport for London fares during his final year as London mayor. The same freeze has been in place for the past two years.

The prime minister said: “Because of the difficult decisions that we have taken to repair the economy, we have been able to hold down commuter fares for the past two years.

“If elected in May, we would freeze them in real terms for the next five. Under Labour, commuters were hit with above-inflation rises year after year. And if they got in again, the chaos they would wreak on the economy would ensure that it happened all over again.”

In the years before the freeze, regulated rail fares could rise by RPI plus 1%. This led to sharp increases in rail fares when inflation was relatively high. The RPI rate currently stands at 1%.

The Tories hope their pledge to oblige companies to offer workers paid leave for voluntary work will show the party’s compassionate side. Cameron will pledge to introduce legislation to implement the new rule.

Bear Grylls, the adventurer and chief scout, said: “Any initiative that encourages people to volunteer is good news. Volunteering changes people – and not only those on the receiving end. That’s the magic of giving: we often get much more in return.

“All of us struggle to find extra time and that’s why to have firm government support that enables millions to volunteer is a huge step forward towards building solid communities all around the UK.”

• This article was amended on 10 April 2015 to correct the figure for the current RPI rate.