Gordon Brown has pledged to do "whatever is necessary" to preserve the United Kingdom in the face of demands for Scottish independence.
Labour has not had a good week in the wake of the Scottish independence referendum row, a UK Government minister has admitted.
Speaking to the Sunday Telegraph, the prime minister urged pro-Union parties, businesses and trade unions to fight to prevent the break up of the UK.
But Scottish Office minister David Cairns insisted the party was united in its stance against the SNP.
His remarks come after Scottish Labour leader Wendy Alexander called for an early referendum on independence.
Scottish Labour leader Wendy Alexander called on Scottish ministers to bring forward its 2010 referendum plans.
She claims she was calling the SNP's bluff, but they ridiculed the move.
Prime Minister Gordon Brown pledged to do "whatever is necessary" to preserve the United Kingdom.
In the newspaper interview, Mr Brown publicly backed Ms Alexander, describing her as an "excellent leader" of Labour in Scotland.
But, in an interview with the Sunday Telegraph newspaper, Mr Brown gave his backing to Ms Alexander, describing her as an "excellent leader" of Labour in Scotland.
However, he went on to stress he was personally "not persuaded" of the case for a poll.
Ms Alexander also repeatedly denied stating in an earlier BBC interview Mr Brown had endorsed her move to call for the early referendum.
Some issues are bigger than politics and need to be addressed in the common interest Gordon Brown
Some issues are bigger than politics and need to be addressed in the common interest Gordon Brown
He said: "I will do anything and everything to ensure that the case for the Union, which has served Britain and the British people so well, is properly heard and advanced.
Meanwhile, a week after Ms Alexander's comments, Mr Cairns told BBC Scotland's Politics Show: "This hasn't been a good week for us and my thoughts are with the hundreds of thousands, of not millions, of Labour voters who are wondering what on earth is going on."
"I want all unionist parties and all parts of business - employers, managers and trade unions - to work together not only to push the case for the Union but to expose the dangers of separation.
But he added: "In the end, what matters is, can we as a Labour party look to our supporters and say, 'do we have your best interests at heart? Do we have the best interests of Scotland at heart? Do we all believe Scotland is better in partnership with our friends and our colleagues and our relatives in England and Wales and Northern Ireland.'
"Everyone in the Labour party believes that with a passion."
Mr Brown, who failed to explicitly support Ms Alexander's position in the Commons, stressed he was personally "not persuaded" of the case for a poll.
He said: "I will do anything and everything to ensure that the case for the Union, which has served Britain and the British people so well, is properly heard and advanced. "
'Grudge and grievance'
The prime minister went on: "I want all unionist parties and all parts of business - employers, managers and trade unions - to work together not only to push the case for the Union but to expose the dangers of separation.
"Some issues are bigger than politics and need to be addressed in the common interest."
"Some issues are bigger than politics and need to be addressed in the common interest."
Last week, Ms Alexander threw Labour into turmoil in both Scotland and England with her unexpected call for an immediate referendum, having previously said that a poll on independence was unnecessary.
International Development Secretary Douglas Alexander, one of Gordon Brown's closest allies and Ms Alexander's brother, told the BBC's Andrew Marr programme he did not believe now was the right time for a referendum.
She later said Labour might introduce its own referendum bill in the Scottish Parliament if the SNP would not - apparently contradicting her earlier opposition to a vote.
He added: "The SNP were elected under a manifesto of having a referendum, but they've made very clear in their response to what Wendy's said this week that they have no intention of bringing forward a referendum until they've fermented more grudge and grievance."
The prime minister failed to explicitly support her when taunted in the Commons about the row by Tory leader David Cameron.
Ms Alexander said her party had 'called the SNP's bluff'
International Development Secretary Douglas Alexander, one of Gordon Brown's closest allies and Ms Alexander's brother, told the BBC's Andrew Marr programme he does not believe now is the right time for a vote.
"I'm not convinced that now is the time for a referendum," he said.
"But I recognise, as Gordon Brown said in an interview this morning, that those of us who believe profoundly in the United Kingdom have to contemplate what steps are necessary to secure the UK against those who want to break it up.
"The SNP were elected under a manifesto of having a referendum but they've made very clear in their response to what Wendy's said this week that they have no intention of bringing forward a referendum until they've fermented more grudge and grievance."
Wendy Alexander has now said that as a minority party in the Scottish Parliament, Labour cannot force an early referendum on its own.
'Indefensible actions'
"The SNP can never again claim that a Unionist cabal is denying Scotland a voice," she claimed.
"The SNP party colour is yellow and now we know why.
"Alex Salmond's supposed timetable for a referendum in late 2010 merely serves his own narrow political and electoral interests, rather than the interests of the Scottish people."
Mr Salmond ridiculed Ms Alexander's "complete and utter humiliation" and said Mr Brown had demonstrated "a supreme inability to either control events or even keep up with them".
Mr Salmond also stressed that Labour had now conceded the principle of a referendum.
And Scottish Tory leader Annabel Goldie observed: "Wendy Alexander tries to defend her indefensible actions of the last seven days by rewriting history, stretching credibility and taking the public for fools."
