Boost for Miliband as 70% leave door open for party while 42% say that they would never vote for a Tory government

Labour has the biggest pool of potential voters of any of the three main parties, despite its opponents' claims that it was guilty of disastrous economic mismanagement in government, a poll shows.

The YouGov survey for the centre-left thinktank IPPR, which suggests that Labour's "toxicity" factor is lower than feared by some in the party, will offer encouragement to Ed Miliband as he seeks to build confidence in his leadership after exactly a year in the job.

In a telephone poll of 2,474 adults, 70% said they might be prepared to vote Labour, as opposed to 64% for the Liberal Democrats and 58% for the Tories. Just 30% say they would "never" choose Labour compared with 36% for the Lib Dems and 42% for the Tories. This suggests that the Tories, not Labour, are the most "toxic" party.

Many senior Labour politicians are gloomy about their party's ability to win back support quickly, believing that attacks on them over the economy have struck home with large sections of the electorate.

IPPR/YouGov poll on voting intentions. Photograph: Giulio Frigieri

These figures, however, suggest that, despite Labour's bruising last few years in government, the damage may be reparable. Nick Pearce, IPPR's director, said: "Labour still has a mountain to climb and a huge task to recover its economic credibility, on which its electoral prospects rest above all else. But this polling shows that Labour is not so damaged that it has lost the potential to be a popular, truly national party, with appeal across the social classes."

The poll is not good news for the Lib Dems, with only 5% of those questioned describing themselves as "core" supporters. Lib Dems normally claim to have a core support of around 12% of the electorate. Some 24% describe themselves as core Labour voters and 19% as core Tory voters.

On the downside for Labour, the YouGov poll shows the party still faces a tough task in rebuilding the broad coalition of support that won it three consecutive elections under Tony Blair.

In the south of England, 40% of people say they would "never" vote Labour, compared with 33% who say the same about the Tories and 35% for the Lib Dems – 23% of people say they would "definitely" vote Tory compared with only 16% for Labour and 7% for the Lib Dems.

Among those over 60 – a higher proportion of whom vote than other age groups – again 40% say they would "never" vote Labour, compared with 37% who say the same about the Tories and 43% for the Lib Dems. More than a quarter – 27% – say they would "definitely" vote Tory, compared with 22% who say they would certainly back Labour and 5% who say they would definitely vote Lib Dem. Among C2 voters, Labour is now the least unpopular party, with just 29% saying they would never vote Labour, while 42% of C2s say they would never vote Lib Dem and 47% say they would never vote Conservative.

While Labour support is often considered weak in the south of England, the new poll shows that the party's position there is not as bad as that of the Tories in the north and in Scotland. While 40% of voters in the south say they would never vote Labour, 49% in the north and 57% in Scotland say they would never vote Conservative. In London, just over a third of voters say they would never vote for each party (34% Labour, 35% Conservative and 37% Lib Dem).

In recent "state of the parties" polls, Labour has been between two and eight points ahead of the Tories, with the Lib Dems at less than half the level they obtained at the last general election. But many in the party believe that, with spending cuts biting, they should be forging further ahead.