Britain's rail companies have designed a fares system aimed at bleeding dry three types of travellers: commuters who have to travel in the rush hour; anyone who needs to catch an inter-city train urgently; and foreign tourists. And in no other industry are the customers who pay the most treated with such disregard.

In a few weeks we'll find out just how bad the next round of ticket increases will be. The train companies have been given the freedom to raise prices using a formula based on RPI for the past decade on "regulated" fares (such as many commuter routes) and charge whatever they like for "unregulated" fares, which include many long-distance tickets.

That the train companies are still allowed to use RPI as the basis for pushing up fares is scandalous in itself. You might think inflation is 1.8%, because that's the last figure reported by the Office for National Statistics. But that was the CPI measure. The train companies use the RPI figure each July to set the following January's increases, and given that it was 2.6% in June, we can expect fares to go up by double the current rate of wage growth in the UK.

It will push the price of annual season tickets past £5,000 a year for growing numbers of travellers. For example, the cost of a Tunbridge Wells to London zone 1-6 ticket is likely to rise from £4,900 to around £5,025. Continental Europeans will (rightly) be staggered at what are now some of the highest fares in the world. The French pay a third of this for commuting, the Italians a tenth.

It's worth noting just how much fares have risen under this otherwise anodyne-looking formula. In January 2011 they went up 6.2%, in 2012, 5.9%; in 2013, 4.2%, and last year, 2.8%. Throughout that period, many workers have been lucky to get a pay rise at all.

In the unregulated part of the market, where no price caps apply, the train companies have nakedly adopted "yield management" techniques akin to a tout outside a gig screwing you for as much as possible.

If, say, you have a family emergency and need to travel urgently, they know you have almost no choice but to pay a bloated price for a "walk-up" ticket that bears no resemblance to the costs they are incurring. Similarly, they dump lots of super-off-peak tickets at very low prices – such as the £3 Birmingham to Edinburgh we feature this week, travelling at just after 6am. These discounts allow the train companies to argue that average prices have not risen much. Indeed, the Rail Delivery Group (a union representing train company bosses and shareholders) told me this week that rail tickets have risen just 6% over the last 15 years, in real terms. "You know everyone will just laugh at that," I said. But they insist it's true.

The rail companies bang on about the vast infrastructure investments Network Rail is making as one reason for fare rises. But take a look at financial information published by the Office of Rail Regulation in April this year, covering spending by the rail companies in 2012-13. It shows that infrastructure spending actually fell in 2010-11 by 4.5%, and only crawled back up by 2.3% in 2011-12.

The cost of running Britain's railways (currently £12.3bn) rose in real terms by just 0.1% between 2010-11 and 2011-12, a period when real passenger revenue jumped by more than 10%.

In reality, fare increases aren't really paying for infrastructure but are instead covering the gradual withdrawal of government subsidies, which have fallen by 9% in real terms since 2010-11. Passengers are also paying for the vast profits made by the rolling stock companies formed at privatisation. Just one, Angel Trains, made £372m in 2013 by its measure of underlying profitability.

It's good to know where your fare increases are really going.

• This article was amended on 6 August 2014. An earlier version said the formula for rises in rail fares was based on the retail price index plus 1%. The formula is now RPI plus 0%.