Defending Labour's achievements in power will not be enough to win a fourth term in power, former home secretary Charles Clarke has warned.
Writing in Labour journal Progress, Mr Clarke claims Labour has "wasted" the first half of the current parliament because of "inner-party" conflict.
He believes changes are needed to demonstrate to the public that Labour is capable of entrenching its approach and values well into the 21st century.
"It seems to me that Labour still remains very unclear about our approach, both in this parliament and the next," Mr Clarke writes.
"Now, above all, we need clarity in each policy area. The current uncertainties are widespread, debilitating and give ammunition to our opponents.
"Whatever the specifics, we must all understand that rhetoric about past Conservative failures and past Labour success will not disguise a failure to face the future effectively."
Mr Clarke says the stakes are high as the next election approaches. He identifies four post-war cycles of party political dominance, including the Thatcherite years and that of new Labour.
He warns: "If Labour gets it all wrong (and the Conservatives get it all right) the next general election. will become the next major turning point, leading to more than a decade of Tory power."
The former home secretary made clear on BBC Radio 4's The World at One programme his article was not an attack on prime minister Gordon Brown, whom he was seen as opposing during his time in the Cabinet.
"My point today and in my article today isn't about Gordon Brown's leadership specifically - as I say, through the whole first half of this parliament, when Tony Blair was leader for most of it, we suffered from this problem," he explained.