The description is in an email exchange between maritime director Tony Middleton and commercial operations manager Shankar Ramanathan in November, a week after Deputy Premier Andrew Stoner announced the plan.

Mr Stoner touted the floating helipad as a ”new signature experience” for tourists and business visitors who would fly on and off it from different sites on the harbour.

But in the November 27 email headed ”Sydney Harbour helipad”, Mr Middleton asked Mr Ramanathan ”in confidence – what are the survey requirements for a floating helipad?”

Mr Ramanathan replied that ”due to the high-risk nature of the operation” his officials would have to adapt overseas standards including those the British Civil Aviation Authority applied to offshore helicopter landing areas.

The memos, obtained under government information public access laws, make plain that the company given permission to operate the service, Newcastle Helicopters, did not have a vessel for the helipad when Roads and Maritime Services officials granted it an ”aquatic licence” for the service on November 8.

Mr Stoner had announced the service would go ahead the next month from an ”innovative new flat-top powered barge”.

But the documents show Newcastle Helicopters had no such barge and was initially going to run the flights from a modified decades-old pontoon that had once been a floating dance hall for Luna Park.

Aaron Shaw, managing director of Sydney Seaplanes at Rose Bay, said he was astonished the government had approved the helipad idea before it had even checked what kind of vessel it would operate from.

A spokeswoman for Roads and Maritime Services said: ”The proponent would have been required to put forward an appropriate vessel. Otherwise they would have not have been able to proceed with the operation.”