London's Mayor has advised planners to reject proposals for a new skyscraper.
In April, the City of London Corporation (CLC) approved the 1,000ft (305m) Tulip tower proposed for Bury Street, beside the Gherkin tower.
But Sadiq Khan said a number of concerns raised in a London Review Panel report meant it would harm the skyline and had few public benefits.
Those behind the project said they were "disappointed" and have a right to appeal the mayor's decision.
Mr Khan advised CLC planners to reject permission on the basis of reasons outlined by the panel, which included:
- The design did not constitute the very highest quality of design required for a building in the location
- The proximity, height and material would have a negative impact on the Tower of London World Heritage site
- The space around the proposed building was insufficient to be safe and to prevent overcrowding
- A lack of new cycle parking spaces failed to comply with the London Plan for transport
The London Review Panel concluded The Tulip "does not represent world class architecture, it lacks sufficient quality and quantity of public open space, and its social and environmental sustainability do not match the ambition of its height and impact on London's skyline".
A spokesperson for the mayor said Mr Khan had "a number of serious concerns with this application and having studied it in detail has refused permission for a scheme that he believes would result in very limited public benefit".
The Foster + Partners-designed tower was to be built at 20 Bury Street.
The CLC Planning and Transportation Committee had supported the plan by 18 votes to seven after conditions were imposed such as restricting ticket sales during peak hours.
Responding to the mayor's recommendation, architects Foster + Partners and developers J Safra said: "The Tulip Project team are disappointed by the Mayor of London's decision to direct refusal of planning permission.
"We will now take time to consider potential next steps for The Tulip Project."
The applicants have the right to appeal directly to the Secretary of State for Housing, Communities and Local Government within six months if the CLC goes ahead and refuses planning permission.
The government department may also step in and direct the CLC to hold off a refusal for a period it specifies.