The latest annual rise in train fares has been met with frustration by both passenger groups and rail campaigners.
They claim the 3.4% average increase is unfair because it has been introduced amid a freeze on fuel duty and is outpacing earnings.
Anthony Smith, chief executive of independent watchdog Transport Focus, said: "As many passengers return from their festive break, rail fare rises will bite as wages continue to stagnate.
"Satisfaction with value for money varies widely. Annual season ticket commuters in London and the South East are among the least content."
He also said that whilst welcome investment is being made in the railways, "passengers need to be able to rely on the trains today."
Bruce Williamson, spokesman for campaign group Railfuture, said: "Fuel duty for motorists has been frozen for seven years now, but not rail fares, which have risen by more than 30% in that same period.
"The Government is showing undeniable bias against the rail traveller and driving people on to our ever more congested and polluted roads."
Sadiq Khan has lent his voice to the debate, saying: "It is simply not right that millions of rail passengers face eye-watering fare hikes today after suffering 12 months of delays, cancellations and disruption.
"Commuters have been hit with fare increases of around 5.5% in the last two years while their cost of living also continues to rise.
"It's time for the Government and private rail companies to step up and give the passengers the service they deserve at a price they deserve."
The Mayor of London has pledged to freeze all bus and tram fares and single pay-as-you-go fares on Tube services until 2020.