The cheapest ticket is in fact the pounds 20 return from London's Marylebone station using the Chiltern train company.
Reporter: "Is that the cheapest fare?"
Operator: "I just put in the details you requested. For Birmingham the computer just throws up New Street from Euston."
Reporter: "What about Birmingham Snow Hill, that is a ten minute walk from New Street."
Operator: "Oh yes. You can leave at 6.30 in the morning ... The cheap day return from Marylebone on that route. That is only pounds 20."
Reporter: "So why didn't that come up as the cheapest ticket?"
Operator: "The computer only shows New Street station when you put in Birmingham. You need to tell me which station in Birmingham, otherwise I can't give you the cheapest fare."
t An Independent reporter posing as a passenger tries to get the price of a ride for which there is no fare.
Merely by pretending to want to end up in Lockerbie, which normally involves a change at Edinburgh Haymarket, a passenger from London can get a cheaper ticket than the standard London to Edinburgh fare.
According to the rules - set out in the rail regulator's routing guide - tickets with loopholes like this should not be sold. But the reporter is told the fare exists.
Operator: (after 30 rings)
" 12 o'clock from King's Cross, arrives at Haymarket at 16:44. Get a connecting train that departs at 17:14 and arrives 18:10 at Lockerbie."
Reporter: "How much?"
Operator: "pounds 53 return."
Reporter: "Where is Haymarket?"
Operator: "I'll have a look ... Oh, actually it is above Lockerbie. You have to go up to Edinburgh and then come down."
Reporter: "That means I can get a pounds 53 ticket to Edinburgh?"
Operator: "(Laughs ...) Oh no, that's at least a pounds 60 saver. I don't know why that happens. I don't make the fares up."
Reporter: "So I can save pounds 10 every time I go to Edinburgh by pretending I am going to Lockerbie?"
Operator: "(Nervous giggle ...) It is odd but I don't know who makes the fares up."