The Big Question: How is progress towards London 2012 going, and are there any hidden pitfalls?

(PA)

Why are we asking this now?

Yesterday marked three years to go until the opening ceremony of the London Games in 2012. That's 1,095 days, or 156 weeks, including today.

The day was marked by a host of media calls on the Olympic site in Stratford, east London, and the first time trial of the Eurostar "Javelin" shuttle service connecting London's St Pancras station with Stratford. The train completed the journey in six minutes and 45 seconds, 15 seconds ahead of schedule.

What spin are the organisers are putting on the progress so far?

Predictably enough, Lord Coe, the former Olympic gold medallist and prominent Tory who is chairman of the organising committee (LOCOG), made it clear that organisers were on course to complete the Games on time and on budget. "We are a little bit ahead of being bang on target," said Coe.

As Britain plunged into recession 18 months ago, and a growing band of sceptics questioned whether the country could afford to spend £9.325bn on a two-week sporting binge (as the critics derided it), organisers defended the Games as the very summit of Keynesianism, stoking demand through investment. Olympic Minister Tessa Jowell described the project to this newspaper as "economic gold at a time of economic need". That mantra was out in force yesterday, as it will be all the way through to the Games, and after them, too.

What have they not achieved at the Olympic Park?

Very little of the infrastructure that was meant to be built by now has not been built. The biggest failures and shortcomings have been associated with fundraising for the Games, which is a consequence of the worst global downturn for eight decades coinciding with the period when organisers needed to raise cash.

The £1bn Olympic Village is now being funded by the taxpayer, and the £355m media centre is similarly funded. Both were originally meant to be entirely funded by the private sector, but the collapse in demand, and sudden loss of confidence in the private sector, impeded any chance of private sector investment.

What have they achieved at the Olympic Park?

A phenomenal amount. It's difficult to convey just how much waste – toxic and otherwise – was sitting dormant on the Lea Valley site in east London, which is an area roughly the size of Hyde Park. On top of the "milestone" achievements trumpeted by organisers, 30,000 tons of silt, gravel and rubble have been removed from the waterways, and several giant, temporary "soil hospitals" have been erected to aid the process. The Olympic Delivery Authority (ODA), impressively led by Australian chief executive David Higgins and English chairman John Armitt, have largely won over sceptics who said the project would collapse under the weight of recession, and that the milestones would not be reached.

What are these fabled milestones?

The foundation structures of the main stadium, the velodrome, the International Broadcast Centre and the handball and basketball venues are all in place. Seats have been fitted in the main stadium and work on the timber track in the velodrome is under way. The press centre is also nearing completion. Of the 2,800 homes in the village, the majority are structurally complete. The Eton Dorney rowing venue, Broxbourne canoeing venue and Weymouth sailing venue are all finished, and a planning application for the shooting event in Woolwich has been submitted. The energy centre, electricity substation and sewer and pumping station are all fully operational too.

Wasn't the whole project woefully over budget?

It's a popular misconception that the Olympics are over-budget, and those responsible for the bid submitted to the IOC must take some of the blame for this. At the time of the bid, the budget for the Games was £2.4bn. But in March 2007, Jowell announced that the new budget would be around four times that. The increase was partly down to inflation between 2004 and 2012 but VAT, which may account for around £1bn, was also left off. And the security budget, currently hovering around the £1bn mark, rocketed because the day after London won the bid, the terrorist attacks of 7/7 hit the capital. Now, despite raiding their £2bn contingency budget (also left off the original bid), organisers expect the Games to cost around £7.2bn, which leaves them around £2.1bn of wriggle room.

Which venues are costing the taxpayer the most?

The Olympic Village, at just over £1bn, is the most expensive development on the site. Its 2,800 flats will house the 17,000 athletes and officials throughout the games and a new education campus, Chobham Academy, will open in 2013. The media centre will cost £355m, and doesn't yet have a tenant for after the Games, while the main Olympic stadium, whose capacity will be reduced from 80,000 to 25,000 after the Games, is costing £538m. Zaha Hadid's Aquatics Centre, whose undulating roof will be the architectural flagship of the Games, is costing £244m. The Velopark, which will host track cycling and BMX racing, and could be the site of Team GB's greatest successes, is costing £94m.

Is it going to be finished on time?

There is every reason to believe that all of the Olympic site in Stratford will be finished ahead of time, and that the adjacent commercial development of what is being called Stratford City will be complete by mid-2011. Transport developments, from the Eurostar Javelin service that was in operation yesterday to the East London line extension and four new stations on the Docklands Light Railway, are also ahead of schedule.

It can't all be going smoothly. What else might they mess up?

The construction site in east London is the biggest infrastructure project in western Europe, and from a technical point of view the surprising thing is not how much but how little has gone wrong. Still, the administrative and practical scope of the project means there is an infinite number of potential difficulties with each of the venues, and on every inch of the park, that need to be negotiated. Among the bigger worries are security, partly because London is still considered by some as a favoured target for terrorists, and partly because the sheer scale of an Olympic Games makes planning for all contingencies very difficult. Another more ceremonial worry is the torch, whose journey over the past few years has been overshadowed by protesters.

Will London 2012 be on time and on budget?

Yes...

*Construction is well ahead of schedule and the hardest part has been done

*The worst of the global recession is over and the forecasted spend is within the £9.325bn

*No Olympic Games start late; if needs be, the Government will step in to ensure the opening ceremony is on 27 July 2012

No...

*What Donald Rumsfeld (in a different context) called the 'unknown unknowns' may cause further delays

*Private sector investment in the Olympic Park and Stratford City is still vulnerable to the after-effects of the financial crisis

*Concerns over security and the sheer scale of the project could jeopardise the strict schedule