Labour leader Wendy Alexander yesterday backed a referendum on Scottish independence, in a major U-turn intended to call Alex Salmond's "bluff".

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Labour leader Wendy Alexander yesterday backed a referendum on Scottish independence, in a major U-turn intended to call Alex Salmond's "bluff".

Her move represents a sharp change in Labour's response to the SNP poll surge, and its timing was a surprise to colleagues.

It came as Gordon Brown yesterday sought to stabilise his battered authority at Westminster, following poor Labour results in council elections across England and Wales. In TV interviews, the Prime Minister admitted mistakes and said he understood people's concerns about rising food and petrol prices: "I feel the hurt they feel," he said. He hinted the planned fuel tax rise this autumn will be shelved.

Ms Alexander's abrupt shift from opposing to supporting a referendum follows what she called "tactical discussions" within the party about putting the SNP administration under pressure on its referendum proposal.

Declaring support for a poll during this parliamentary session, she drew criticism of "panic" from her unionist allies as well as Nationalists.

Having previously argued a referendum would be a distraction and that it played to the SNP's "obsession", the U-turn has been discussed with Prime Minister Gordon Brown, though not agreed with him.

An insider at Holyrood suggested the abrupt move resulted from Ms Alexander's frustration that the Prime Minister has been slow to commit himself to a strategy on responding to the SNP.

Other MSPs were not aware the U-turn was to be announced yesterday. This came in a BBC interview, after Ms Alexander accused Mr Salmond of running scared of bringing his referendum plan before parliament.

LibDems rounded on their Labour allies on the constitution, saying Ms Alexander was panicking after Thursday's bad election results south of the border, with her new position based "on tactics not principle".

Mr Salmond said that the parties were "starting to crack", warning that if unionist parties did not support a referendum, he would make it "a dominant, transcending issue in the 2011 election campaign".