Campaigners have welcomed a temporary sale on more than one million train tickets across Great Britain, but argue that costs should be cut even further.
The government's "Great British Rail Sale" will see some off-peak prices slashed by as much as half between 25 April and 27 May.
But the Campaign for Better Transport said wider price increases are "driving people off the railway".
Passenger numbers on trains have not yet returned to pre-pandemic levels.
About 285 million rail passenger journeys were made in Britain in the last three months of 2021 – just 62% of the levels seen before coronavirus struck, according to the Office of Rail and Road.
Transport Secretary Grant Shapps said more than one million train tickets would be reduced this spring.
The Department for Transport (DfT) is hoping the move will help struggling households to afford trips across the UK and boost the domestic tourism industry.
It comes after the highest train fare rises for nine years came into force for rail travellers in England and Wales last month.
The sale brings some Manchester to Newcastle journeys down to a little over £10, while seats on some London to Edinburgh services will be slashed from £44 to £22, the government said.
The discounted tickets went on sale for selected advance fares earlier on Tuesday, with passengers able to purchase them from the National Rail website.
The promotion only applies to tickets for travel from 25 April to 27 May, with tickets available to buy until 2 May.
This means the offer will have ended by the time many schools break up for May half term.
And it will also miss the four-day UK bank holiday weekend from 2 to 5 June, which will mark the Queen's Platinum Jubilee.
Tickets covered by the sale include routes in England, Scotland and Wales.
In a video to advertise the sale, Mr Shapps said: "We've had two years of living life virtually. It is time to get real and visit our beautiful country."
To help with the cost of living, we're selling over 1 million rail tickets at up to ½ price for trips from 25 Apr to 27 May 🎫
After 2 yrs of living life virtually, the Great British Rail Sale🚆 starts today.
Get yours here👉 https://t.co/FJmjw54wyZ pic.twitter.com/CyPva6s905
However, some passengers have complained that discounted tickets were unavailable for the route they wanted to travel.
Peter King, 52, was planning to use the sale to buy tickets from his local station, Hockley in Essex, for a day trip to Norwich. There is no direct train so he would normally travel via London Liverpool Street but that route was not included in the sale.
"It was easy enough to get the cheap tickets from London Liverpool Street to Norwich but they were obviously not offering it for what you'd class as the commuter line from Hockley to London Liverpool Street, even though it was off-peak," he told the BBC.
"You're still paying a fair whack just to get to London itself so the offer for me was just no good."
Scott Arthur, 33, was hoping to buy cheaper tickets from London to Liverpool for the end of April. From there he plans to travel on to north Wales for a friend's stag do as there is no direct train.
However, when he searched online he found there were no discounted tickets available. Train operator Avanti told him the promotion only applied to advance tickets and it was likely there were none left for April as it was too close to the departure date.
"For me, it's flawed because if many of the advance tickets are already sold out before the promotion was even announced, that means it's only a few tickets that are available for this offer," he told the BBC.
He added that even with 50% off train prices were still "extortionate", with his trip from London to north Wales costing around £80 in total.
Meanwhile, some commuters said limiting the promotion to off-peak trains meant they could not benefit from the savings.
The Campaign for Better Transport said that it had been pushing for action to improve passenger levels for months.
It welcomed the move by the government, but Norman Baker, its chief executive's adviser and former transport minister, said: "It can show the Treasury that the way to increase income is to cut fares, not keep ratcheting them up and driving people off the railway."
"This initiative, though very welcome, is but a first step," he added, calling for an end to annual fare rises and a review of tickets and travel patterns following the rise of hybrid working during the pandemic.
DfT said reforms to the rail sector through the so-called "Williams-Shapps" plan for rail will mean that network-wide sales of tickets should be able to take place more easily in the future.
But Shadow Transport Secretary Louise Haigh said that in the meantime, the temporary move would provide little respite "to passengers who had thousands taken out of their pockets from soaring fares since 2010."
"And the decision to end the sale just before half-term will mean many families face the same punishing costs over the holidays," she added.
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