THE former Secretary of State for Scotland has hit out at his former cabinet colleague Theresa May as he questioned her ability to lead a future campaign against Scottish independence.

Alistair Carmichael fears Mrs May's government will revert to the battle plan from 2014 - dubbed 'Project Fear' - and fail to learn the lessons that another pro-Union push would have to be "much more Scottish-centric".

He also accused the Prime Minister of using the turmoil over a possible independence vote to try to secure more Tory votes in May's council elections.

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Lib Dem MP Mr Carmichael, who spearheaded the Scotland Office during the 2014 referendum, also warned that a ballot as early as 2018 would be illegitimate.

Speaking ahead of his party conference in Perth, Mr Carmichael said that his vast experience of Mrs May across the cabinet table in the coalition government was that she had a "better sense of self-awareness" than her predecessor David Cameron.

But he warned that she risked repeating Mr Cameron's mistakes by "promoting her party's interest rather than the national self-interest".

He accused her of "playing the nationalists' game" by talking about independence and that she "sees that there are votes in it".

Mr Carmichael raised concerns that the Prime Minister's government will failed to understand that the campaign strategy going into a second vote on Scottish independence would have to be completely overhauled from 2014.

"The biggest danger - and I suspect that No 10 does not really understand this - is [in planning] to fight the last war," he said.

“I don't want to see another independence referendum. But if by whatever means it happens you have to understand that it will be a very different campaign from the last one.

“For most of the last campaign the fairly complacent expectation was that there would be a No vote - right up until the last couple of weeks. That is not going to the case this time.

“Too much of the way in which the campaign was fought allowed to be characterised as a contest between governments in Holyrood and Westminster.

"That cannot be allowed to happen again. It will have to be a much more Scottish-centric campaign.”

But he also accused the SNP of being in a "sort of denial" over independence.

He said that if Ms Sturgeon "goes for another referendum she immediately deepens the polarisation which makes it more difficult than ever for her to get a majority for independence."

But if she did not then she risked "destroying the big tent" the SNP has held together in recent years.

He accused the party leadership of being in a "sort of denial" adding "It is the SNP in ‘La La Land”.

In a BBC documentary broadcast last night, Nicola Sturgeon said that next autumn would be “the common sense time” for a second referendum, if Mrs May rejects a bespoke Brexit deal for Scotland.

But Mr Carmichael said this timeframe would be inappropriate because the UK would still be in the middle of divorce talks with the European Union.

"It is difficult to see how you can legitimately ask the people in Scotland if they want to leave the UK when it is not yet clear what sort of UK you would be leaving," he said.

UK Government sources have also suggested a 2018 ballot would be improper and believe that it could fail one of the keys tests applied to the 2014 vote, which ministers in Edinburgh and London agreed had to be "fair, legal and decisive".

A Tory government insider said last week it was a "big question" whether or not Scots could make a "fair" choice on their constitutional future before Brexit while last night a No 10 spokesman said that there was ”no need for another referendum”.

Mrs May had made clear she was confident about the future of the UK, he added.

Meanwhile, the SNP has accused pro-Union parties of "conjuring up" objections to another vote on Scottish independence.

As Scottish Secretary, Mr Carmichael hit the headlines amid allegations he lied about the leak of a confidential memo which incorrectly claimed First Minister Nicola Sturgeon told the French ambassador that she would prefer to see David Cameron remain in Downing Street at May’s general election.

In the end, a court ruled that he had told a "blatant lie" but rejected an attempt to unseat him as an MP.

During last night's interview, Ms Sturgeon denied that she was bluffing over her willingness to call a re-run of the independence vote if her demand to keep Scotland in the European single market post-Brexit is rejected.

Earlier this week the former SNP deputy leader Jim Sillars said that he he could not “conceive of the Yes movement winning in 2018 in the middle of [Brexit] negotiations".

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In recent days sources close to Ms Sturgeon have tried to play down speculation that she will make a key announcement on a referendum at next week’s SNP conference in Aberdeen.

They suggested that the First Minister would hold back until after Mrs May kick-starts Brexit talks.

However, speculation is mounting in Westminster that Theresa May could trigger Article 50 as early as next Wednesday.

A No 10 spokesman said that Ms Sturgeon's "common sense" comment was not an explicit demand for a second referendum.

But he would not be drawn on whether or not Downing Street would veto a second referendum.