But Culture Secretary Tessa Jowell told the culture, media and sport select committee that the costs for the Games had been planned with extreme "rigour".
Band D council taxpayers are expected to pay about £20 a year for 10 years to meet the cost of staging the Olympics.
Ms Jowell said there would be a "daily vigilance on monitoring the costs".
"What I cannot say is that there will be any guarantee there will be a cap," she added.
The council tax payer, the London Development Agency and the National Lottery are contributing the public sector funding for the Games.
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