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It has long been assumed by experts that the £2.4bn pricetag for the Olympic park was a ludicrously optimistic estimate for the total cost of the Games. But here we are, barely out of the starting blocks, and all that’s been talked about is costs spiralling out of control.

On the plus side, the financial issues are being brought into the open at an early stage, so the construction industry is less likely to be scapegoated for the inadequacies of the government’s accounting systems. Truth be told, that initial bill was a rough estimate based on 2004 prices (which is what the International Olympic Committee actually asked for). And, at the same time, it was the bait that got the public to bite. Now we’re talking about 35,000 extra homes in Stratford, as well as extra security and transport infrastructure, it’s pretty clear that the final bill will be somewhere north of £10bn. And we have no idea where much of that money will come from.

What’s more, forecasting the cost of a project this size is more dark art than economic science. As Graham Matthews, a partner at EC Harris, writes on page 10, the risks are legion. We have no idea how contaminated the ground is, no idea what the stadium will look like, no idea what will happen to interest rates or the planning system over the next six years. And, as Tessa Jowell has already pointed out, the price of steel has been pushed up by rising energy prices and demand from China and India. But then again, nobody knows how much steel will be required …

What we need from the government and the Olympic delivery team is political bravery – both in terms of opening the public purse and standing up to the cynics and killjoys who say the Games will bankrupt London. And in this respect the industry must play its part – if it gets it wildly wrong or fails to have its voice listened to then there will be no forgiveness. It’s vital to set a realistic budget for the true out-turn costs in 2012. And the only way to set a realistic budget with so many unknowns is to build in a whopping contingency fund, and in that respect, Gordon Brown’s 60% figure sounds about right. Budgeting on the basis of the most palatable headlines today won’t do us any favours in the long term. It will drain morale and severely handicap the delivery team – a bit like trying to run the 10,000m in shackles.