David Cameron raises Wendy Alexander's comments at PMQs
Wendy Alexander has said she will not quit as Scottish Labour Leader over her call for an early referendum on Scottish independence.
Her comments came after Gordon Brown earlier failed to explicitly support her stance during question time at the House of Commons.
Rivals said Ms Alexander's position was untenable - but she insisted she had support from party colleagues.
She said it was time to end the uncertainty over Scotland's future.
Mr Brown's comments came after Conservative leader David Cameron accused him of losing touch with reality - and control of the Scottish Labour Party.
The Tory leader told the Commons: "This is what Wendy Alexander said: 'I don't fear the verdict of the Scottish people,' she told BBC Scotland on Sunday 'bring it on', what else could that possibly mean?"
I have the support of the prime minister, the Labour group of MSPs and indeed many MPs and party members in harrying the SNP for the hollowness of [the SNP] position
Mr Cameron asked if the prime minister agreed with Ms Alexander that there should be a referendum now on independence.
He also sent Mr Brown a letter asking him to clarify his stance on a referendum.
"It is not what she has said," Mr Brown replied, adding that Labour, the Tories and the Liberal Democrats had joined forces to set up the independent Calman Commission on devolution.
"I hope we can see progress on that commission and we will review that progress before we make any further decisions," he said.
Responding to Mr Cameron's letter, he added: "Wendy Alexander and I are agreed that all parties in favour of the Union have a duty to expose the hollowness of the SNP's position: claiming they favour independence, yet wanting to postpone any referendum.
"I thought the Conservative Party would welcome such an approach."
The Scottish Government said it would not be hurried into speeding up its plans for a 2010 referendum.
Ms Alexander told BBC Scotland: "The prime minister and I are agreed on the need to expose the hollowness of the SNP's position, which is to claim they favour independence and yet not be willing to bring forward the referendum.
"I have the support of the prime minister, the Labour group of MSPs and indeed many MPs and party members in harrying the SNP for the hollowness of their position."
But Scottish First Minister Alex Salmond said something now "had to give".
He added: "The positions of Wendy Alexander and the prime minister are incompatible. This claimed agreement is clearly not there.
"Either she has to go, he has to go or they both have to go and I suspect he wants to stay so I think she's now in a very difficult position."
Wendy Alexander said it was time to end the uncertainty
Scottish Lib Dem leader Nicol Stephen added: "This is very close to meltdown. Nobody knows what Labour stands for any more and its leadership is in disarray."
Meanwhile, Ms Alexander's threat to bring forward her own referendum bill to Holyrood may fall at the first hurdle because of Scottish Parliament rules.
MSPs proposing legislation need the support of 18 colleagues from at least two of the major parties and rules also state the lawmaking process cannot be started if the Holyrood government of the day plans its own legislation on the same proposal within the parliament's four year term.
Labour MP Brian Donohoe said he wanted a referendum as soon as possible.
The MP for Central Ayrshire said: "I think the people of Scotland have to determine whether or not we allow the situation to bubble on or whether or not we lance it as an issue right now and get on with running the economy of the country, which I think the public believe is more important."
Sir Kenneth Calman, chair of the devolution commission, also issued a statement reinforcing that party leaders and UK ministers still backed the body, after some questioned its relevance amid the debate on the timing of a referendum.
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