What will be the true cost of London 2012?
Pointing to the £500m of contingency untouched in the last three months, Robertson said he was as confident as he could be that the Games would not exceed the £9.3bn public sector funding package.
Today's report by the Public Accounts Committee seems to agree with him, with PAC chair Margaret Hodge insisting the Games are "on track to be delivered on time and within budget".
But then the report also contradicts that assessment by arguing that the true cost of the Games could be nearer £11bn once the £766m price tag for buying the Olympic Park land and £826m of legacy projects are taken into account.
The true cost of the 2012 Games could yet be felt in London's nearby financial district. Photo: Getty
For example, there will inevitably be security costs beyond the £475m set aside in the Olympic budget. If that money comes out of the Metropolitan Police or Home Office budgets, should that be considered an Olympic cost?
And what of the funds spent by other government departments, such as the Foreign Office, whose job it will be to look after visiting dignitaries and heads of state. Is that an Olympic cost?
It used to be sufficient for the government to say the £9.3bn was an infrastructure budget, set up to pay for the venues of the Olympic Park.
But with that money now being used for so many different areas of the project - security, ceremonies and other operational requirements associated with the actual staging of the Games - that argument no longer holds.
So in that sense it is right that the PAC should question whether the real bill is much higher and to call for a full and thorough audit of all the public money that has been spent on putting on the Olympics when the Games are over.
On the two specific points raised by the PAC, the Department of Culture, Media and Sport is clear that they should be treated separately to the £9.3bn.
It says the £766m for the land acquisition will be repaid once the site is sold after the Games. Less convincingly perhaps, it argues that the £826m for legacy projects comes from "existing business as usual" budgets.
Most people will look at all this and find it meaningless to quibble over which department is spending what on the Olympics. Ultimately, it all comes from the same source and "Olympo-cynics", as Boris Johnson calls them, will say it is money that should not have been spent at all, especially when there is such a squeeze on the public finances.
The PAC report also flags up concerns about the pressure on the budget of the London Organising Committee of the Olympic and Paralympic Games (Locog), which was always supposed to be a separate and entirely privately-funded enterprise.
But almost £1bn of public money is now being spent through this committee (Locog), while the PAC says the government, as the ultimate guarantor, could end up on the hook for even more money.
With this in mind, it is still worrying that, despite all this taxpayers' money being pumped into the Locog, it remains subject to less scrutiny than government departments and publicly funded bodies like, say, the Olympic Delivery Authority.
Locog has already been heavily criticised by the London Assembly for being overly secretive on the controversial issue of ticketing. Perhaps the time has come for London 2012 officials to become much more open with us.