Last month the Mayor and Transport for London announced the appointment of a contractor to build the scheme.
They also confirmed that, despite previously suggesting no public money would be spend on the project, Londoners would have to meet the expected £57m construction costs.
TfL will then seek to recoup costs via sponsorship deals including selling naming rights.
The Mayor was responding to a question from Liberal Democrat Caroline Pidgeon at Wednesday’s Mayor’s Question Time who wanted to know then the car would be “open to passengers”.
Declining to give a date, the Mayor told Pidgeon the scheme would be completed when “it’s good and ready”.
The Mayor had previously expressed hope that the scheme could be operational in time for next year’s Olympic Games.
Speaking after the meeting Pidgeon said: “It is simply staggering that the Mayor is throwing around £57 million of public money at the Thames Cable Car yet is totally incapable of giving any assurance as to when it will be open.
Pidgeon called on the Mayor to “get on top of this flagship project.”
