"That's not the number of employees at the convention centre. That's the number in the whole economy. Some will be at the convention centre, some will be in the hotels and some will be additional taxi drivers."
The company was contracted by the Ministries of Economic Development and Tourism and the former Auckland City Council to produce the study.
It was summarised in a September 2009 report which included interviews by Government officials of convention centre managers in Australia and Asia.
Mr Key has championed SkyCity's involvement in the convention centre deal since discussing it at a dinner with the firm's directors in 2009.
He has cited new jobs as one benefit of the centre, telling Parliament last month: "The SkyCity convention centre would create about 900 jobs in construction and 800 jobs working your way through it."
A press release from the Beehive set the number of construction jobs at 1000 and staff employed at the centre at 800.
Mr Hamilton said: "I think people have misunderstood or misinterpreted what some of these numbers mean and the difference between total employment and new employment."
He also questioned the construction job figures, saying: "I'm not quite sure what the source of that 1000 was."
The original Horwath report said 150 jobs could be created over a five-year construction period for a total of 750.
Mr Hamilton said it was possible more people would be needed to build the centre but such workers were already employed on other construction projects.
Mr Key is in Europe and was unavailable for comment. A spokesman for Economic Development Minister Steven Joyce said additional advice had been sought.
He said the convention centre would put $90 million a year into the economy and support up to 1000 jobs during construction and about 800 new jobs once it was running.
"The numbers of construction jobs are based on those created over the life of the construction project and figures include advice from the construction industry."
Talks between the Government and SkyCity over the deal have dragged on for almost a year. SkyCity was chosen to build the centre after it offered to pay the $350 million construction cost in return for being allowed hundreds of extra poker machines, new table games and an early renewal of its Auckland casino licence.
The Government said earlier that the job numbers came by dividing the estimated wage bill by the $30,000-a-year average salary of workers in the sector.
Unite Union national secretary Matt McCarten said the likely wage for convention centre staff would be between the minimum of $13.50 an hour and about $15 an hour. "I just find it hard to believe there are that many jobs."
Green Party co-leader Metiria Turei said the doubt over the numbers showed the Government argument in support of it was "flimsy and dodgy".
