Only one in four voters believe Labour leader Ed Miliband has what it takes to become PM, even though most would vote his party into power.
Labour's popularity has dwindled to a 12-month low with voters uncertain about the party's ability to form the next government, according to Ipsos MORI.
The Opposition is still well ahead of the Conservatives, who are languishing on 29%, but support has fallen from previous highs to 38%.
Overall, 58% of British adults doubt Labour is ready to form the next government while 66% do not believe Miliband is ready to be prime minister.
Although the number of voters that believe he can take on the job has increased by 7 points since May 2011 to 24%, the figures are "significantly below" the poll ratings Tony Blair and David Cameron were scooping at a similar point in opposition, according to Ipsos MORI.
The news may come as a blow for Miliband who said recently it was "possible" he could become prime minister.
The negative view of Miliband is not echoed amongst some of his peers. Earlier this week Tory MP Conor Burns compared him to the late Margaret Thatcher.
There is little good news in the findings for the Liberal Democrats, who are on 10%.
While all the major political parties are struggling to boost support, Ukip's performance continues to hold up, with the party maintaining its highest level of support - 15% - in an Ipsos MORI poll.
Ukip leader Nigel Farage came out as the least unpopular party leader, with 26% dissatisfied with his performance compared to dissatisfaction rates of 65% for Lib Dem Clegg, 60% for Cameron and 50% for Miliband.
Tom Mludzinski, deputy head of political research at Ipsos MORI, said: "While Nigel Farage and Ukip may take good news out this poll there is little joy for anyone else. Labour are at a 12-month low as voters have doubts that Ed Miliband and his party are ready to move into Number 10. While he does have two years to change their minds, even his own supporters are not yet fully convinced."
- Ipsos MORI polled 1,010 adults aged 18+ across Britain by telephone between April 13-15 and the findings were weighted