As thousands of commuters across Britain renew rail season tickets this week, consumer rights groups have warned they face an opaque system designed to make them stump up for the most expensive option.

Annual passes for passengers travelling into London cost thousands of pounds, but an analysis by The Independent has found consumers are not given clear information about the savings available from different types of tickets.

The official Season Ticket Calculator tool on the National Rail Enquiries website only compares the average price per journey on an annual pass compared to a weekly ticket, ignoring other options that may be more suitable for passengers.

Consumer rights watchdog Which? is leading calls for a more transparent system. It called the process “too complex” for passengers to find the best option for them.

In all cases the customer could also have saved money by opting for a monthly pass instead of a weekly one – but the tool did not list what this saving would be.

One ticket office operator at Bishop’s Stortford told The Independent an annual pass gets customers “12 weeks for free”.

But they only made the comparison between the fee for a weekly pass instead of a monthly one.

An example of what is shown to commuters on the National Rail Enquiries website

The operator also suggested taking out a 0 per cent credit card in order to manage the debt of getting an annual ticket up front.

Barry Doe, a leading independent expert on rail fares, said monthly passes “could even be cheaper [than annual] per journey if the month has 31 days”.

He added: “I’ve no idea why they don’t push this.”

Mr Doe said there needed to be greater transparency for passengers. “Buying tickets on the web is still appalling in general,” he said. “When it comes to seasons people ought to be told clearly of the week, month, annual differences and ratios and the advantages of annuals.”

Bruce Williamson from the campaign group Railfuture said it was already hard enough for passengers to get the best deal from the “expensive and complex” array of rail fares.

“We're concerned that this looks like another example of passengers being directed towards the most expensive option rather than the one which is best for them,” he said.

And Which?’s director of campaigns and communications, Vickie Sheriff, told The Independent: “Rail passengers often struggle to find the cheapest fare as the current ticketing system is too complex. Train companies need to be clear and upfront on how passengers can get the best deal for them and transparent about what these savings are based on.”

Annual passes do often end up being the best value option for commuters who know they will be making the same journey consistently over the whole year.

But factors such as the timing of annual leave and the availability of cash up front means each passenger needs to be able to weigh up their own options fairly.

Megan French from MoneySavingExpert.com told The Independent: “Annual passes are often good value for most, but it’s worth commuters doing their own calculations to see which type of ticket works best for them. They should factor in things such as annual leave, part-time or working from home options, and if any part of the journey is during off-peak times.

“Once they have found their best option, then look at the cheapest way to buy the ticket, taking into account any options such as season ticket loans from employers, for example.”

A spokesman for the Rail Delivery Group, which runs the National Rail Enquiries website on behalf of train operators, pointed out that customers can claim a refund on any unused months on their annual season ticket.