The London 2012 Olympic Games should cost no more than £6.5 billion, according to PY Gerbeau - almost £3 billion less than the present estimate.

Mr Gerbeau, formerly a bid adviser to Barbara Cassani, who first led London's successful 2012 bid only to be dropped in favour of Lord Coe, said that he had watched in horror as the bill for the Games had soared to £9.3 billion.

He believes that the complicated organisational structure around the Games and the Olympic Delivery Authority is one reason that the bill has risen beyond expectations.

“We should have London 2012 plc: one central board and directors who are accountable for what they do. The more opaque the structure is, the less responsible people are ,” he said.

As a former French Olympian - he played ice hockey - Mr Gerbeau is full of praise for Britain's medal success in Beijing, but he believes that the team's achievements should not be used to squeeze more money out of the Government for the Games.

“The saving grace for London 2012 is the success the team has had in Beijing. But we must not raise expectations that more money will bring more golds,” he said.

Mr Gerbeau took on the challenge of making the Millennium Dome a financial success after Jennie Page, its first chief executive, was dismissed. However, he repeatedly had to ask the Millennium Commission for millions of pounds in grants to keep the doors open. He ran the East London venue for a year.

By the end of 2000 the cost of the Dome had spiralled to almost £1 billion. The original lottery grant for the facility was £400 million.