It won't matter whether it's red, yellow or blue. Every general election manifesto in 2009 will proclaim social justice. These are topsy-turvy political times: other parties are stealing New Labour's political clothes while Oliver Letwin's old friends in the Thatcherite think-tanks dub him "Oliver Leftwing" for arguing that a Tory government should support redistribution to narrow the gap between the haves and have-nots.

As the Fabian Life Chances and Child Poverty Commission shows, Britain today is marked by stark inequalities from cradle to grave. Child poverty has fallen, having increased from one in seven to one in three from 1979 to 1997. But over three million children are growing up in poverty in Britain today. After missing its first interim target this month, the Government must change gear to meet its commitment to halve child poverty by 2010 and eradicate it by 2020. The new cross-party "battle for social justice" presents Labour's next leader, Gordon Brown, with both a more serious electoral threat and a political opportunity for his ambition to forge a "progressive consensus".

"Reform to tackle inequality" could be the slogan for an agenda to unite progressives. A life chances "litmus test" for policy would ask whether a measure would improve life chances for the disadvantaged most of all? Does it narrow the gap between them and the rest? That should be the test of schools admissions policies and health funding.

To win a public argument about inequality, Labour must make this "life chances" approach central to next year's comprehensive spending review, when Mr Brown will make the political decisions on which the next general election will be fought.

Can talk of social justice be converted into a more equal Britain? Only if an emerging political consensus has at its heart a shared commitment: we must make child poverty history at home, too.

Sunder Katwala is the general secretary of the Fabian Society. 'Narrowing the Gap,' the report of the Fabian Life Chances and Child Poverty Commission, will be published on Thursday.