Leading article: With the Olympic Games over, the trickier task begins

With the world's athletes heading for home and Britain's great Olympic party over, the question of the legacy of London 2012 and its £9bn price tag begins to come to the fore. Judged on sporting prowess, on drama, on public mood, the Games must surely be considered a spectacular success. Ultimately, however, they will also be measured against rather tougher criteria.

That Lord Coe has been appointed as legacy "tsar" should hardly come as a surprise. In experience, commitment and sheer drive, he is an obvious choice to play a central role in ensuring that the Olympics were not just 16 days of awesome sporting and logistical achievement but also make a lasting contribution to Britain. Nonetheless, the swift action from the Prime Minister in announcing Lord Coe's new role before the revels were even over suggests a desire to ensure that the confidence of the Games themselves carries straight on into the task of what comes next.

Lord Coe is certainly a fine choice. His achievements, first in putting together London's winning bid, and then in so spectacularly delivering it, deserve both our praise and our gratitude. To a significant extent, Britain's triumph as a host was down to him. But his new job will, if anything, be even trickier than the old one.

It is a promising sign that Lord Coe will continue to have the ear of the Prime Minister. But David Cameron will need to do more than just listen. Part of the reason for the success of London 2012 was the absolute commitment from the very top of the Government. Failure was simply not an option: witness the swift drafting in of the military when the security company G4S fell so disastrously short.

For the legacy to be as compelling as the Games, Lord Coe will need similar support. Too often, high-profile policy tsars with nothing to trade upon but their names struggle to make much real impact. But Lord Coe will need similar powers to those he is used to if he is to make real headway on such thorny issues as the guarantee of "affordable" housing developments in the former Olympic park or the vexed (and often expensive) question of sports facilities, particularly in schools.

Meanwhile, the most conspicuous challenge is the still unanswered question about the future of the main stadium. After 18 months of back and forth, the plan is now for the stadium to be leased, rather than sold, with West Ham football club as the favourite. But there are those that query its ability consistently to fill so many seats. And with sceptics already muttering darkly about white elephants, the danger of a mothballed stadium becoming the emblem of London 2012 is looming large.

Alongside the plans to regenerate Stratford and "inspire a generation" to take up sport, there are also other, rather more unexpected, consequences from the Olympics. Amid the festivities of the past weeks, the G4S debacle has been overshadowed. Now, with the Games concluded, questions as to how much – or even if – the company should be paid will rightly return. But it is the shift in the balance between the private and public sectors that will have more profound repercussions. That no less a figure than Philip Hammond, the Conservative Defence Secretary, is reconsidering his assumption that outsourcing is always best is not only a measure of the impact of the fiasco, but also has significant implications for future military policy. Quite an outcome for a sporting event, even a global one.

The Paralympics are, of course, still to come, and it can only be hoped they will be as much of a success. With tickets rapidly selling out, the signs are good. But the serious business of the Olympic legacy is already under way.