The Olympics in 2012 will be the largest sporting event hosted by this country.

When the UK Olympics Committee made its bid, the budget was set at around £3.5billion. In November 2005, the Secretary of State for Culture, Media and Sport told the House of Commons that the Government believed the budget was sound. This was confirmed by Chancellor Gordon Brown's in his annual pre-Budget report just a few weeks later.

Despite these assurances, in the last 18 months the budget for the Olympics has run out of control. It has now almost trebled to more than £10 billion.

I find it staggering that the original budget was signed off by Mr Brown without any thought being given to whether VAT would be payable and without providing for a contingency fund. These two costs alone add more than £3.5bn to the bill.

Writing in this newspaper over a year ago, I warned that security costs had been underestimated. The original bid included a sum of less than a third of what the Greek authorities spent in 2002 after the 9/11 terrorist attacks. Security costs have now been revised up from £220m to £600m.

I recently challenged the Chief Secretary to the Treasury in the Commons as to why the costs of the Olympics had escalated. He could not promise that there would be no further increases in the budget.

While Londoners are not yet being asked to foot the bill for the cost over-runs directly through council tax, Mayor of London Ken Livingstone has not ruled out extending the 12-year period when Londoners will pay extra council tax to pay for the Olympics.

Furthermore, Mr Livingstone has agreed to fund a further £300m from his regeneration and capital budget. That £300m could have been spent improving London's ailing transport network such as the troubled Northern Line or the congested A406.

The Lottery Fund has been told to stump up another £675m. While the Government claims that this should not affect existing projects, many groups in Barnet could lose out on their future bids.

It is nothing less than incompetent for Mr Livingstone and Mr Brown to allow the Olympic budget to spiral in this way. The two largest cost overruns, VAT and contingency, were entirely predictable at the time of the bid. Now the National Lottery and the taxpayer are being raided to pay for Gordon Brown's mistakes.

If the costs can treble in just one year, despite clear assurances from ministers about the robustness of the budget, what confidence can we have that the Government will not ask for more money in the five years before the Games take place?

The key thing now is for the Government to put a full, open and transparent budget in the public domain so that everyone knows who is paying for what - and stick to it.

This will do more than anything else to restore public confidence in London 2012. Montreal took 30 years to pay off the debts from its Olympics.

Let's hope we are not doing the same in 30 years time.