Deputy Labour leader Harriet Harman has called the Conservatives "arrogant" for believing it is "their turn, their right to lead this country".
She closed Labour's conference by claiming Tory policies were "a wrecking ball that would demolish the economy".
Ms Harman criticised Liberal Democrat leader Nick Clegg too, saying the British people would not "trust him even with their loose change".
But she praised Gordon Brown, calling his conference speech "brilliant".
The equalities minister also renewed her attack on the Sun, a day after the newspaper's decision to switch its allegiance to the Conservatives.
Delivering the closing speech at the Brighton conference She said: "We are not going to be told by the media that it is the Tories' turn, the Tories' right, to lead this country.
"A free press is an important part of our democracy. It must be free and it must be fair. The press does not decide who will govern this country. The people do."
She said: "We leave this conference with a clear sense of direction... with a new sense of determination. The choices are set out.
"We are determined. We are committed. Together we'll fight for those we represent. Together we'll fight for a prosperous and fair Britain. And most importantly, we'll fight to win."
Conservative Party chairman Eric Pickles responded to the speech by saying the important choice at the general election next year will be "between a tired and discredited Labour government that offers them no new ideas, and a Conservative Party that has the policies to rebuild our broken economy, mend our broken society and fix our broken politics".
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.