Hundreds of rail ticket offices are facing closure under a cost-cutting measure that will force passengers to use ticket machines and risk being overcharged.

The Government is preparing to approve the closures, despite receiving evidence from the passenger watchdog that people find machines confusing and prefer speaking to ticket clerks for advice on the cheapest option.

Clerks are legally obliged to offer impartial advice whereas machines simply display long lists of ticket options without explaining which is the most suitable. Passengers who fear being fined for having the wrong ticket may feel compelled to buy a more expensive ticket without realising that cheaper options are valid.

Machines continue to offer peak and off-peak tickets even after the times when much cheaper “super off-peak” fares become valid. Restrictions on ticket validity are becoming even more complex from today, with each train company having different definitions of the peak and off-peak periods.

South West Trains, Britain’s biggest train company, is planning to reduce ticket office opening hours at 114 stations. Many will close all weekend and open for only a few hours on week-day mornings. Other companies are also planning to close many of their offices if the Department for Transport approves SWT’s cuts. More than 500 stations nationally could either lose their offices altogether or have opening hours drastically reduced.

Many types of ticket are not available from machines, including extensions beyond the station originally booked, many tickets to stations beyond the franchise area and tickets starting from other stations. Railcards cannot be bought from machines, so passengers needing to renew them would have to pay the full fare to get to a station with a ticket office.

A study by Passenger Focus, the government-funded rail watchdog, found that many passengers preferred to queue at ticket offices rather than use nearby machines with no queues.

The watchdog said: “The conscious decision to purchase at ticket offices is largely driven by the purchaser’s lack of confidence in using the machine.”

It concluded: “In the absence of staff to advise, passengers using ticket machines may be unfamiliar with the validity of ticket types, as a result of which they may end up choosing the wrong ticket.”

They might either pay too much or “buy the cheapest ticket and risk paying a penalty fine”. The watchdog added: “Older customers in particular may be alienated by a wider introduction [of ticket machines].”

Gerry Doherty, the leader of the TSSA rail union, said: “By replacing booking clerks with machines, the companies not only save on labour costs, they can also sell more expensive tickets. Without the impartial advice that staff are obliged to provide, customers will be forced to buy a more expensive ticket from machines.”

He said the DfT’s decision on SWT’s proposal would determine the future of ticket offices across the country.

“We fear that this could be the green light for every other franchise to try to maximise profits as passenger numbers fall during the recession.”

An SWT guard said: “I regularly come across passengers who have paid too much at machines without realising it. People are so scared about being fined that, if in doubt, they will opt for the more expensive ticket. I have raised this repeatedly with the company but they tell us to concentrate on catching fare dodgers.” The guard said that some of the cheapest tickets were not sold by machines. “People don’t know about these tickets but a clerk would tell them if they went to a booking office.”

SWT said it had invested £12 million in machines, adding that passengers wanting advice on tickets should ring its call centre. A spokeswoman said that SWT might remove expensive peak tickets from the list offered by machines after the peak.

“Every machine would have to be finessed but it could be considered.”

Times recommends

• Dubai cheaper than Doncaster as room rates tumble
• World Cup 2010 - how to follow England
• Copenhagen: Europe's greenest city