Michael Moore has played down the possibility of the UK Government taking legal action if Holyrood runs its own independence referendum.

The Scottish Secretary said he did not "envisage the circumstances" of Westminster raising an action in the UK Supreme Court despite the hard line taken by Advocate General Lord Wallace who warned a Scottish Parliament Bill to organise a referendum without Westminster's approval would not be legal.

But Mr Moore yesterday adopted a more conciliatory tone to that of his party and UK Government colleague.

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He said: "There is no threat from the UK Government. But what I'm saying is that anybody in the country could do that challenge. Why would we risk that?"

Pressed on whether he was ruling out the possibility of the UK Government taking the case to the Supreme Court, Mr Moore said: "I don't think that would be the right way forward. In the circumstances that we are in, what is very important is to ensure that we get the two governments working together to get the powers resolved and beyond doubt."

He said once the terms for a legal, fair and decisive referendum were agreed there could be more discussion on what independence would look like under the SNP.

Mr Moore is proposing to transfer extra powers under Section 30 of the Scotland Act to ensure a "fair, legal and decisive" ballot, but the move is expected to come with preconditions, which Mr Salmond rejects.

Mr Moore was also challenged on who would lead the fight for the Union. He said: "That will emerge over time, but I think you will see on the side of the argument of those who want to stay in the UK a much broader based team of people."

One of the men expected to be at the forefront of the pro-Union campaign, former Chancellor Alistair Darling, said there was "no point spending an awful lot of effort" in discussing how to improve devolution until after the referendum.

He said it would be "relatively easy" to hand over income tax powers and added: "What you would want to do is to get to a situation where if Scotland decides to spend money on whatever, it then has to decide whether taxes have to go up.

"This is something that is essential for the future, but the big question that we have to answer now is are we staying in the United Kingdom or not?"

SNP MSP Humza Yousaf said Mr Darling had taken Labour into the "same camp" as the Tories. He said: "It is a ridiculous position for Labour to take and is profoundly anti-democratic. David Cameron and Labour are both now advocating a campaign of no information for the people of Scotland in terms of their alternative to independence."

LibDem leader Willie Rennie accused the SNP of "woolly fantasy" after Justice Sectretary Kenny MacAskill said if there was a "yes" vote there would be "aspects where we would return to the people of Scotland".

Mr Rennie said: "When the Scottish people vote in the referendum they need to know the full details of the SNP proposals. Kenny MacAskill implied this would not be the case. The SNP are in a state of flux on so many issues relating to Scottish independence. They need to come clean on what Scottish independence will mean for our future."

Meanwhile, a former Labour spin doctor claimed Gordon Brown missed the chance to outmanoeuvre Mr Salmond by failing to back the ex-Holyrood leader Wendy Alexander's "bring it on" call for a snap referendum.

Simon Pia said Labour MSPs had been dismayed when he backed off. But Mr Pia admitted Mr Brown had "never fully committed" to the idea.