Train passengers across the UK are facing above-inflation fare rises of up to 11% on Wednesday.
Regulated fares, which include most season tickets, are going up by an average of 4.8%, and many unregulated fares are set to rise by much more.
Consumer groups said the rises were unjustified, but train operators said they were needed for improvements.
The rises come as services on the West Coast Mainline continue to be disrupted by over-running engineering works.
Rises 'will rankle'
Train operators said the average rise of unregulated fares - such as cheap day returns, advance purchases and long-distance open tickets - would be 5.4%.
But rail consumer watchdog Passenger Focus said some fares had gone up much more than this, and warned that many passengers would be irritated.
For example, it said an annual season ticket from Gillingham in Kent to London was going up from £2,496 to £2,740 - a 9.78% increase.
The same from Canterbury to London was rising from £3,132 to £3,480 - an 11.11% increase.
Chief executive Anthony Smith said: "Steep rises on individual routes are masked by the average figures published by the industry.
"This will lead to passengers having to dig deep into their pockets. These unjustified and unfair rises will rankle."
Peter Andrew, a regular commuter on First Great Western trains and a spokesman for rail campaign group More Trains Less Strain, told BBC Radio 5 Live there would not be much "merriment" at his station at the rises.
"We've still got the same late and unreliable trains, as we had before. We've still got the same late and overcrowded trains that we had before... And now we hear that the fare is going up."
'Brand new trains'
But George Muir, director-general of the Association of Train Operating Companies (Atoc), said the rises were necessary.
"The revenue from fares helps pay for investment that directly benefits passengers," he said.
"Billions of pounds are now being spent to improve the railway and the results are showing through."
And John Willman, business editor of the Financial Times, said the extra money was being well spent.
"Nobody's going to be pleased to be paying more," he told BBC Radio 5 Live.
"But on the other hand they will be riding on trains that are far, far improved since rail was privatised 15 years ago... There are brand new trains. They're much smoother, much faster. The services are much better. We're travelling on better trains than ever before."
Record passengers
The Conservatives say rail passengers are "paying the price for the government's complete failure" to reduce fares and other costs associated with the UK's railways.
And the Liberal Democrats said ministers seemed "content to force up train fares as a way of limiting demand rather than providing the rail network which is needed for social, economic and, most of all, environmental reasons".
And Stephen Joseph, executive director of the Campaign for Better Transport - formerly Transport 2000 - said: "These fare spikes are bad for people and bad for the environment."
But a Department for Transport spokesman said: "Passenger numbers are at record levels, making a nonsense of suggestions that people are being priced off the railway.
"This growth, along with sustained investment by the government, is helping pay for major investment in the network."
BBC NEWS | UK | Rail fare rises come into force