Miliband told he has 12 months to make himself a credible leader

There is just a year left for Ed Miliband to turn himself into a credible prime minister-in-waiting, according to research to be published by the Labour-affiliated Fabian Society this week.

Polling and focus group discussions suggest that Mr Miliband trails David Cameron in the leadership stakes because he has the wrong qualities for today's difficult economic times. Voters judge Mr Miliband to be a "good listener", but regard being decisive and a good communicator as more important – areas in which the Prime Minister outguns him.

Next week's Labour conference marks his first year in the post of party leader, so the research contains a ray of hope for Mr Miliband: it found that the "critical" period for a leader of the opposition is his or her second year in the job. For example, Mr Cameron's and Margaret Thatcher's personal ratings fell during their first 12 months, but they still went on to become prime minister.

While insisting there is "all to play for", the research report says Mr Miliband remains a largely unknown figure to many voters, with 60 per cent surveyed saying they don't know what his qualities are. It says: "Swing voters are telling us Ed needs to define himself as a leader and fast."

The research, to be published in Fabian Review, was carried out by Deborah Mattinson and Ben Shimson as part of a study on leadership in business and politics for BritainThinks, a new strategy and polling company.

They found that, in 2006-07, "listening" was the top quality the public sought in a politician after the MPs' expenses scandal. Now anxiety about the economy means people want "decisiveness and communication". Mr Cameron and Mr Miliband are level on "integrity", but the Prime Minister has a clear lead on being decisive and a good communicator.

Today Mr Miliband will discuss plans to dilute the trade unions' influence inside his party at a meeting of Labour's national executive committee. Len McCluskey, leader of the Unite union, warned he would not give Labour a "blank cheque". He told Red Pepper magazine: "The Labour Party can only exist if it speaks on behalf of ordinary working people and organised labour."