Harriet Harman warned that Labour must not fight the Tories "in the gutter" as she sought to draw a line under the Damian McBride smears affair.
After a week in which politics has been dominated by the resigned Downing Street aide's emails, Labour's deputy leader said there was no place in politics for personal attacks.
"Labour stands for principles and values," she told activists.
She continued: "Whatever anyone else does, we will not fight in the gutter. No-one in the Labour Party wants to see us involved in personal attacks. The Prime Minister has made it clear that this has no place in politics.
"So we will have nothing to do with smearing the Tories. But we will take them on, on their polices - past, present and future. The way to win is to fight on our values and principles."
Ms Harman went on to try to reinvigorate the Labour ranks, insisting they could be "confident" in the party under Gordon Brown's leadership.
Ahead of what are expected to be difficult local and European elections for Labour on June 4, the party's deputy leader promised that Tory leader David Cameron's "phoney" policies would be exposed by then and sought to emphasise the premier's "conviction" leadership on the economy.
"I think now is a time for us to be confident and for us to be determined," she said.