IN A leadership contest in which two brothers hogged all the attention, many people thought Labour's best performer was actually Ed Balls. The shadow education secretary is another forty-something professional politician with dark hair and a curious intensity about him, but he offered qualities his rivals did not. A speech he gave in August on the danger to the economic recovery from the government's austerity plan was the most acclaimed of the race. He landed blows on Michael Gove, the education secretary, over the government's schools-reform policy. And instead of the last-placed finish some expected (and hoped) for him, he came third.

But while Mr Balls's combination of intellect and aggression will make him an asset to Ed Miliband, his new leader, he could also prove hard to handle. For a start, he craves the shadow chancellorship. If he gets it, he may turn all economic policy into his personal fief—as did Gordon Brown, his old mentor, who once almost made him the real chancellor of the exchequer. As he is a less zealous deficit-cutter than many of his colleagues, never mind his opponents, this could provoke splits. If he does not get the job, his disappointment could turn to mischief. Mr Balls is better liked than in his years as Mr Brown's henchman, but he has retained his sharp elbows and a reputation for plotting.

Compounding all this is the rumour that Mr Balls does not think much of Mr Miliband. The pair were colleagues in Mr Brown's entourage, but Mr Miliband was very much the junior one. Mr Balls prides himself on intellectual rigour and political clarity; Mr Miliband is said to strike him as soft-headed. They also speak for different wings of the party on issues such as crime and civil liberties. Mr Balls, whose fan base is in Labour's working-class heartlands, comes from the no-nonsense camp. Mr Miliband is part of the metropolitan left that regarded New Labour as overly authoritarian.

This has implications for Mr Balls's future. Some think that he would be cannier to ask for the job of shadow home secretary. He would relish bashing the government as posh liberals wringing their hands over popular policies such as CCTV and sending lots of people to prison. Tony Blair made his name in that post. But that stance would be hard to reconcile with Mr Miliband's softer views. Meanwhile, his furious opposition to the government's plan for “free” state-funded schools might also make it hard for Mr Miliband, who wants to leave his options open on that issue, to keep Mr Balls in his current role.

For all the credit he has earned since May, when his stock sank because of his links with the defeated Mr Brown, Mr Balls's finest hour may be to come. More than any other politician, he has cautioned that austerity could kill the recovery. If he turns out to be right, the vindication could propel his career. His party may even look to him as a future leader.