Poor advice from rail staff could mean some passengers paying more than double the cheapest train fare, according to an investigation by Which? magazine.
A team from Which? asked station ticket office staff and National Rail Enquiries Service (NRES) staff about the cheapest way to take specific turn-up-and-go journeys by train.
Two in three station clerks and two in five NRES staff failed to quote the cheapest fare.
Where there was a choice of train company, Which? was quoted the more expensive fare 27 out of 50 times, with 80 per cent of station ticket offices ignoring the cheaper option.
In some cases, the fare quoted was more than double the cheapest available option. Asking about the the cheapest way to get from London to Grantham in Lincolnshire, Which? was quoted a £57 fare on National Express East Coast when the best option was a £22 journey on First Hull Trains for a journey departing around the same time.
When asked about making the same journey twice in one week, two thirds of staff gave the price of two returns, although a rover or season ticket would have been better value.
More than half the questions about breaking a journey en route were answered incorrectly. When asked about journeys close to the end of a peak period, staff tended not to mention that delaying the time of departure - sometimes by just a few minutes - could result in savings.
Which? also checked how efficient lost property offices were, and found that five out of 16 train stations failed to contact owners when a coat and wallet clearly labelled with a name and phone number was handed in.
At one station, at Luton in Bedfordshire, the coat was returned to the owner, but not the wallet or the cash it contained, with staff unable to explain what had happened
Which? magazine editor Martyn Hocking said: "If you just want to know the cheapest way to get from A to B, you'd expect staff at the station ticket office or on the end of the rail helpline to be able to tell you.
"It's not acceptable that passengers could be paying well over the odds because of poor advice. Rail firms must ensure that staff are properly trained and that fare information is clear."
When Which? checked the quality of rail fare advice in 2007, station staff answered 60 per cent of questions correctly and call centre staff answered 40 per cent correctly.
Michael Roberts, chief executive of the Association of Train Operating Companies, said: "This report is seriously misleading. Independent research last year, using a sample of passengers 50 times the size used by Which? and based on the kind of questions most commonly asked by passengers, found that the correct information on rail fares was given 99% of the time.
"To help us improve how we handle queries, we have asked Which? to provide us with the actual questions it posed but, for the second time, the magazine has declined to do so."