Lord Mandelson has warned Labour it must reach out beyond its core vote if it is to win the general election in just five months time.
The former business secretary and veteran of the Blair and Brown governments said on Monday evening that Ed Miliband had an opportunity to become prime minister, but only if he captured the "centre ground" of British politics from David Cameron and the Conservatives.
Labour, he said, must be "reaching beyond our core". And he cautioned that voters would not respond to a politics "motivated by envy" of those who were wealthier.
The 2015 election in May looks to be one of the closest in a generation. Polls have placed Labour ahead of the Conservative Party, however it is not a commanding lead. A Lord Ashcroft survey published yesterday gave Labour a one-point advantage over the Tories, 31% to 30%.
Mandelson said: "There is no point in just talking to Labour voters, because, put simply, there are not enough of them to win an election by depending on our current Labour voters alone."
"Our message can be got across to a wider constituency than the one we have at the moment. I do believe the Conservatives can be beaten at the next election. I wasn't always of that view. I rather felt in the past that probably one term would not be sufficient to replace them before the coming election and we needed to be more than a one term opposition," he said.
Mandelson acknowledged Britain could be heading for another hung parliament and that it was a "six party race". He indicated majority Labour or Tory governments were unlikely in the near future, although "they may eventually return".
"At the next election, to win power, parties need to put together alliances of voters from different parts of the spectrum and different parts of the country. No party that wants to win power at the next election can afford to consign or just simply not bother with groups of voters from different parts of the country, to my mind that would be an act of great self destruction."
Mandelson told the gathering of Labour MPs, candidates and activists at a Policy Network event in parliament that George Osborne's Autumn Statement and plans for further spending cuts had created an opportunity for Labour. "People are not at all sure what sort of country we will even be living in where the country will need up in a further projected £55bn of state spending reductions," he said.
He said the "ideological relish" with which the chancellor wanted to cut spending was "not where mainstream voters are" and would cost the Conservatives votes.
However he warned Miliband, who has focused much of his offer to voters on the "cost of living crisis" and the unfairness of Tory spending cuts, that Labour also needs to convince voters it can sustain economic growth.
"The temptation for Labour is to concentrate on the fairness and social justice dimensions, but in my view the implications for our longer-term economic capabilities in this country on which future social justice hangs are just as great and both need to be emphasised," he said.
Analysing the voters up for grabs in 2015, Mandelson said: "They want policies that are aspirational they aren't motivated by envy or resentment of those who are better off. They want workers to be treated fairly in their pay and conditions, but what they don't like is 'them and us' approach to politics, or a mentality where you are being forced to make a choice for the bosses or for the workers."
Looking back at Labour's previous time in power, the former cabinet minister and European commissioner joked: "We may have lost our way 2009/10 when I came back, sorry about that".