Ed Miliband could seize power with just 35 per cent of the vote, senior Labour figures calculate.
Advisers to the Labour leader say a coalition of core voters and disaffected Liberal Democrats could put him in Downing Street.
They point out that Tony Blair secured his third term in office with just over 35 per cent of the vote.
Supporters claim the so-called '35 per cent strategy' would allow Mr Miliband to ignore the concerns of Middle England and focus on the demands of the unions and the Left.
But the idea dismayed the party's remaining Blairites, who warn it would be disastrous to ignore the needs of the majority of the country even if they were not vital to secure power.
Supporters of the approach believe Labour's core support is about 29 per cent of the electorate, with Lib Dem defections likely to boost that figure by at least six per cent in 2015.
With the Lib Dems scuppering attempts to reform Britain's electoral system, Labour also still enjoys an inbuilt electoral advantage.
Details of the plan emerged as Mr Miliband moved to kill off a Blairite revolt against his leadership.
Mr Miliband has struggled to hide his irritation at an intervention from Mr Blair last week in which he warned Labour was in danger of becoming a protest party.
The two men will hold private talks this week in a bid to agree a public truce.
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But, at a meeting of Labour MPs, Mr Miliband made it clear he had no truck with Mr Blair's criticisms.
'New Labour was formed 19 years ago,' he said. 'Tony Blair taught us the world changes, and the world does change, and we will learn our lessons.'
Minority: The 35 per cent strategy would allow Mr Miliband to focus on demand of the unions and the Left
He likened Labour to a football team that is 'ahead at half time... with the ball still at our feet'.
One supporter of the Labour leader dismissed Mr Blair out of hand. 'When did Tony Blair last knock on doors in Redditch?' the MP said.
'I'm not sure how much he knows about what the British public feel from the first-class lounge at Heathrow Terminal 5.'
Irritation: Tony Blair warned last week that Labour was in danger of becoming a protest party
But former Home Secretary David Blunkett - one of a number of former Cabinet ministers to back Mr Blair - last night said: 'The idea that you don't learn from a leader who won three elections is risible'.
Sources close to Mr Miliband last night insisted he would not pursue a strategy that targeted only 35 per cent of the voters. 'There is no 35 per cent strategy,' the source said.
But the Labour commentator Dan Hodges said the approach was being actively discussed at the top of the party.
He added: 'For all the talk of One Nation, Labour's leader thinks that if he can convince just 35 per cent of voters to give his party the benefit of the doubt in 2015, he'll win. Tony Blair is not alone in thinking it's a strategy that is fundamentally flawed.'
Former Tory treasurer Lord Ashcroft said the 'unambitious' 35 per cent target showed that Mr Miliband knew Labour's opinion poll lead was 'soft'.
He said Labour appeared to be 'turning away from reality' by opposing every cut put forward by the Government.
In a further development the former minister John Denham - champion of the argument that Labour must win in the South of England - yesterday resigned as Mr Miliband's Parliamentary aide.
Mr Denham said he wanted to focus on beefing up Labour's campaign in the South. He dismissed the idea that Labour should pursue a 35 per cent strategy even if that could deliver power.
'The whole challenge for us is not just to win our target seats but to establish ourselves again as a significant political force in the south of England. Our ambitions go way beyond our target seats