Energy Secretary Ed Miliband warned the Scottish Labour conference in Dundee that both Britain and the Labour Party are facing "testing times".
He stressed the need for Labour values in these tough economic times, but warned delegates: "We need to be honest here in Dundee and say what we all know - which is that we face testing times for our party and more importantly testing times for our country as well."
Mr Miliband also stressed the need to "embrace nuclear power as part of our energy mix" and said coal could be a "fuel for the future not just a fuel for the past".
The "green revolution" taking place across the world, he went on to say, could help create new jobs.
Prime Minister Gordon Brown was criticised over plans to part-privatise the Royal Mail by a union official.
John Brown, Scottish secretary of the Communications Workers Union, reminded the conference the prime minister had told them privatisation and deregulation were not the answer to economic problems.
"Why is the government legislating to privatise the Royal Mail, which will ultimately lead to the loss of tens of thousands of jobs across the UK," asked Mr Brown.
Work and Pensions Secretary James Purnell warned Labour of the need for party unity in the face of "turmoil" that lay ahead.
He told the conference: "Amidst the turmoil we will face over the months ahead, we will have to answer a question as a country and a party - will we stick together and use our unity to build a better world than we had before, or will we let our fears force us apart?
Mr Purnell went on to pledge Labour would do all in its power to fight unemployment, and accused the Tories of opposing spending an extra £2bn on helping those out of work.
Labour MSP Jackie Baillie is to bring a backbench bill to Holyrood that would create an NHS "hospital superbug commissioner".
Health spokesman Cathy Jamieson, who announced the move during her conference speech, said the commissioner would be key to pulling together the various agencies responsible for fighting hospital infection.
The call came following the death of 18 patients at the Vale of Leven Hospital in Dunbartonshire, following an outbreak of Clostridium difficile.