During their combative, often bitter rivalry, the former Mayor of London, Ken Livingstone, has fallen out with Mayor Boris Johnson over buses, Tube fares and policing the streets.

Now the cost of visiting central London's Shard, the English capital's latest tourist attraction, is becoming another bone of contention.

Livingstone has called on his successor to subsidise trips to London's tallest building to ensure the original vision of public access to the tower is guaranteed.

The Shard's viewing floor opens on February 1 with the cheapest adult tickets at £25 ($47.60), if bought online, £30 if bought in person and £100 for immediate, unbooked entry. A child's ticket costs £19. The former mayor believes the charges will price many would-be visitors out of a trip up the tower as they outstrip entry fees for the Eiffel Tower (£12/$23), Empire State Building (£16/$30) and the Leaning Tower of Pisa (£14/$26).

The view from the Shard is also considerably more expensive than other London attractions. The cheapest ticket for the London Eye, the giant Ferris wheel on the south bank of the River Thames, is £17.28 ($33), while the Tower of London is £18 ($34) but there is a family ticket at £47/$90.

Livingstone, Mayor from 2000 to 2008, has been a vociferous backer of the 310m-high glass-clad pyramid, which was built near London Bridge by architect Renzo Piano. At 95 storeys, the Shard is the tallest building in Europe, although the viewing deck's height cannot compete with the Eiffel Tower's or Empire State's.

"I saw the Shard as being like the Empire State Building," said Livingstone. "Unfortunately, everything in London is expensive and the job of the mayor should be to reduce some of the effects on people. We are living in a dual world in London where half the people cannot afford to visit places like the Shard. This is why we campaigned for so long to have free museums," he said.

As Mayor, Livingstone introduced a scheme in 2001 allowing every London pupil one free visit to London Zoo. Johnson cancelled the scheme in 2011.

"If I was mayor, I would extend the London Zoo scheme to include the Shard to ensure that it can be enjoyed by more people," he said.

Travel specialists agreed ticket prices were high compared with similar attractions. Joanna Kirby, the publisher of the Rough Guide to London, said: "The Shard may have unparalleled views of London but most other London sites offering scenic views of the capital, such as the Tower of London and St Paul's Cathedral, are also steeped in history so could be considered better value for money."

Clifton Wilkinson, editor of the Lonely Planet Guide to London, said that, in spite of the price, the attraction was sold out for its first two days. "People are excited by it now but only time will tell if it has longer-lasting appeal," he said.

Andy Nyberg, chief executive of View From the Shard, defended the prices.

"It is comparable to other attractions. We are offering a queue-free experience. If you go to similar places and pay for a queue-free ticket, it's about the same price," he said. "In the Shard we have a 21st century tower across the river from the 11th century Tower of London."

$47: Cost of online ticket for adult visiting London's Shard

$23: Ticket for the Eiffel Tower

$30: Trip up the Empire State Building

- Observer