The claim was made by Stephen Greenhalgh, deputy mayor for policing and a contender to replace Mr Johnson at next year’s mayoral election.
Last month Mr Greenhalgh promised to slash fares by 3% a year if he becomes mayor, reversing seven years of above inflation increases under his boss.
Writing on ConservativeHome, he today said: “I want London to have the best public transport in the world. At the moment, however, we also have the most expensive.
“Notwithstanding the different pricing models in other cities, the plain fact is that London has higher fares than New York, Paris or Tokyo.”
Mr Johnson has repeatedly denied such claims when made by opposition politicians and has previously defended the “record level of investment” his increases have delivered for the bus and Tube networks.
Speaking last month, Mr Johnson told this site that potential successors were free to take their own decisions over fares but said his “are based on what is best for the city.”
Val Shawcross, Labour’s transport spokesperson on the London Assembly, said: “Finally a senior member of Boris’ inner circle has admitted that under his mayoralty travel in the capital has become the most expensive in the world.
“Under Boris Johnson fares have increased each and every year with overall fares up over 40% since he came to power.
“Whilst Stephen Greenhalgh is right to say the capital’s transport costs are the most expensive in the world, it’s incredibly hypocritical that he says he would bring costs down after serving in Boris’ top team for years.”
Green Party AM Darren Johnson said: “The Mayor and Transport for London have been in denial about this for years and their business plan still relies upon annual above inflation fare rises to pay for things like tube upgrades and Crossrail.
“The problem is that fares are already too expensive and that is starting to drive people back to car travel, rather than using public transport. The roads system is going to clog up with extra traffic unless we have both public transport investment and also lower fares.”
Caroline Pidgeon, the Liberal Democrat leader at City Hall, suggested Mr Greenhalgh’s efforts should be focussed on his role overseeing the Met.
She said: “Comparing public fares between cities around the world is incredibly difficult and sweeping general statements are rarely helpful. What is certain is that Stephen Greenhalgh has a full time day job of being Deputy Mayor for Policing and Crime.
“With London experiencing a worrying spike in murders since the start of this year I suggest Londoners cannot afford to have a Deputy Mayor for Policing and Crime whose key priority seems to be his own political career.”
Asked about Mr Greenhalgh’s article at Mayor’s Question Time, Mr Johnson said those looking to reduce fares would need to identify “which investments they would cut” but added that his deputy was entitled to express his views.
