You already know how to get a refund from a train company if they've mucked you around, thanks to our guide. We suspect there might be a few people in the suburbs of London who might be getting on it this week, after an investigation showed that they were being royally ripped off.

It looks like some rail passengers are being charged four times the amount of a correct fare for journeys across the capital. Please add a 'train company rip off shocker - NEXT!' comment below this article.

So what's happening? When people are being sold 'anytime' tickets for travel within London, often, Oyster fares would have been hugely cheaper, say Campaign for Better Transport. They noted that Ewell West in Surrey, run by South West Trains, a passenger was asked to pay £19.50 to travel to Theobalds Grove in Hertfordshire, when an off-peak Oyster fare would have been £5.20.

There's a number of other fares that would have been significantly cheaper if they'd been offered an Oyster fare.

Rail campaigner Martin Abrams said that, during his investigation, station staff told him passengers were receiving the inflated fares because their computers aren't showing Oyster fares. Very convenient.

Abrams said: "The fares system in this country is hopelessly complicated, so much so that even a computer system can't work out the cheapest fare. This problem can't be blamed on new stations being brought into the Oyster zone as some of these stations have been in the Oyster zone since 2010."

"This is a failure of the train operating companies, and their fares and ticketing technology needs to catch up quickly if passengers are to have any confidence that they are capable or indeed willing to sell the cheapest appropriate ticket for their journey."

The Association of Train Operating Companies, who represents the assembled companies that run the railways, say that you should try and get a refund if you think you've been stung.

A spokesperson said: “The rail industry has worked with Transport for London (TfL) for many years to bring cheaper travel to train passengers using Oyster cards. This is an issue affecting a handful of stations recently added to TfL fares zones and the industry will fix this problem as quickly as possible to ensure that the correct fares are in the system."

“People using Oyster cards to travel to these stations will have paid the correct fare. For other passengers, maps at stations and in ticket offices display information telling them they can use their Oyster card, but unfortunately it is still possible that some people could have been sold the wrong fare.

"We’d urge anyone who thinks they may have been sold the wrong fare to contact the place from which they bought it to seek a refund.”