Ananova:

Cabinet minister Harriet Harman will put class at the heart of the political battle, as she tells unions that it is the key factor in determining individuals' life chances.

Ms Harman will announce a year-long investigation into inequality which she said would provide an "authoritative" analysis of the gaps between rich and poor in the UK.

And she will say that the overarching influence in inequality was the issue of "where you live, your family background, your wealth and social class".

The announcement was greeted with scorn from Conservatives, who said that Labour had presided over a decade of growth in levels of extreme poverty.

A report earlier this year from the independent Institute for Fiscal Studies which said that inequality had risen over Labour's decade in power to reach its highest level since 1961.

The slice of national income going to the richest fifth of households rose from 40.9% to 42.6% since 1997 while the share taken by the poorest families dropped from 7.7% to 7.2%.

Ms Harman will tell the TUC Congress at Brighton: "To advance equality through our public policy, we need clarity of evidence and focus on the gaps in society and how they have changed over the last 10 years.

"The robust evidence base that the panel will produce will help us properly target measures to address persisting equality gaps and build on the good work that we have already done."

The Government will come under fresh pressure over its record on equality from trade union leaders in Brighton as the TUC debates attempt to close the gender pay gap. Congress has already delivered strong attacks on the Prime Minister over below-inflation public sector pay rises and the Government's reluctance to impose a windfall tax on the profits of energy firms.

The conference will call for new moves to achieve equality at work including moves to tackle the pay gap between men and women. Public sector union Unison will press for mandatory pay audits to make sure women are not paid less than men for similar work.