Mr Purnell said Labour must reassert its ideological principles
Labour should win the next election as the centre of gravity in British politics has "shifted to the left", former minister James Purnell has said.
Mr Purnell quit the cabinet last summer in protest at the leadership of Gordon Brown, saying it increased the likelihood of a Conservative victory.
But he told an audience in London that Labour should be "confident" of victory if it had a "clear and radical agenda".
Yet he also warned Labour's "absence of ideology" could now prove a handicap.
'Absence of ideology'
The former work and pensions secretary walked out of cabinet last July. He called for a leadership contest, but senior members of the government refused to follow his lead.
Since then, he has sought to kick-start a debate about the future direction of Labour as an adviser to the think tank Demos.
In a speech at the London School of Economics, he argued that "progressive" ideas dominated the mainstream of politics and the opposition was not offering radical change as had been the case at previous elections such as 1979 and 1997.
"The Conservatives' desire to present themselves as progressives is a massive act of flattery to the Labour Party and demonstrates that the centre of gravity in British politics has been shifted to the left," he said.
"This should give Labour strategic confidence as it approaches an election it should, given the circumstances, win."
But Mr Purnell warned that Labour had struggled to build an "enduring coalition for change" since 1997.
As a result, the party needed to state more clearly its commitment to core principles such as tackling inequality and a more "hands-on" approach to markets to tackle "concentrations of economic power".
He urged Labour to be serious in its pledge to devolve more power by backing reform of the voting system and open primaries, opening up school catchment areas and supporting community projects which cannot get state or private funding.
He warned of excessive government intervention into people's lives, citing the example of plans for criminal records checks for millions of people working with children - diluted by ministers in December - as an example of state over-reach.
"If we try to tell parents they need a criminal records check before giving lifts to their kids' friends, we end up stopping people from helping each other," he said.