Leading article: Balls' big idea is a decent first step

So far, the new political season has been dominated by ministerial upheavals and the Coalition's renewed attempts to bring the economy to life. Today, both Ed Miliband and Ed Balls re-enter the fray, hosting a day-long conference on economic policy and making their first joint appearance since reports of seething tensions between them.

In the interview published in this newspaper today, the shadow Chancellor dismisses such speculation as "total garbage". And given that both parties were on holiday when the reports surfaced, on a quiet Bank Holiday weekend, he has some cause to feel bemused. There are bound to be tensions between two very different personalities who served for more than 10 draining years in Gordon Brown's court. It is unlikely, though, that a public feud is on the brink of eruption. Both saw the destructive impact of the Blair/Brown rivalries and, as passing victims of those epic internal battles, they will go out of their way to avoid a repeat.

A much greater challenge is devising policies that are distinct and credible at a time of extreme financial constraint. Wisely, Mr Balls avoids making detailed commitments, asserting only, with justification, that no shadow Cabinet member can make additional spending pledges in the current febrile context.

More interesting still is Mr Balls' revealing hint that he is contemplating the introduction of a mansion tax, to provide extra funding for the NHS and also for skills training. Such a policy would prove significant for both practical and political reasons. As The Independent has long argued, there is a powerful case for a mansion tax, both on grounds of fairness and because of the urgent need to raise revenue which is easily collectable. Politically, Mr Balls sings the praises of Vince Cable, the tax's original proposer, which may perhaps pave the way for a future Lib/Lab partnership.

For Mr Miliband and Mr Balls, the big tests of policy-making and positioning are still to come. But they are starting to show signs of developing an alternative that deserves to be taken seriously.