As ever with Olympic projects, never ever trust the original budget submitted by those keen to win public support for hosting the Games.
The 2012 London Olympics are no such exception, as it turns out that some £250M in VAT payments were "forgotten" in the original budget submission.
Tessa Jowell, the culture secretary whose separated husband faces trial in Italy for fraud, came clean to the Commons and said that London's initial budget did not include the 17.5% cost of VAT on the construction of the venues and infrastructure.
The Treasury, never knowingly shortchanged on tax revenue, needless to say offers no hope of reprieve from this humiliation for the Olympic planners; it claims that its hands are tied by European law, and that the Olympic Delivery Authority (ODA) will have to pay the additional tax bill.
However, Hugh Robertson the shadow sports spokesman said that he had been given a personal "cast iron assurance" about six months ago by Ms Jowell in a corridor of the House of Commons that VAT would be waived on building the Olympic facilities.
Never ever trust Olympic budgets!
Ms Jowell claims that London's bid documents did not include VAT on the construction of venues for 2012, because the ODA had not been established and its legal status could not be anticipated.
Ever heard of contingency budgets Tessa?
In true weasel style, so typical of a politician, she then attempted to avoid responsibility by claiming that London's plans had been endorsed by a cross-government group and issues in relation to VAT were not identified as an issue at that point by the Treasury or by departmental accounting officers.
Mr Robertson said:
"The government is the author of its own problems by not being clear and transparent about the costs of the Olympics. The DCMS thought it had an agreement with the Treasury, but Gordon Brown played hardball and it unravelled. I am sure a solution will be found, but only after causing damage to the Olympic games. It is not doing the Olympic process any good."
Don't trust Olympic budgets, or the politicians who put them together.