The Queen was prepared to intervene before the Scottish independence referendum in 2014 to help boost support for the Union, according to reports.

A new book by Lionel Barber, the former editor of the Financial Times alleges that he was told by the Duke of York just one week before the vote that the Queen was preparing to step in.

The monarch, 94, told people in Scotland to "think very carefully about the future" ahead of the vote, and now Barber has claimed the comments were part of an orchestrated plan to deter voters from backing the Yes campaign.

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"I can tell you that down in London they panicked," he told The Sunday Times.

"There is this scene where I am at Buckingham Palace invited by the roguish Duke of York to lunch with the Chinese foreign minister, and Andrew suddenly half lets loose that the Queen is going to intervene on the Sunday.

"They had clearly planned it... it was very artfully done. I'm sure that David Cameron did the same thing which he later did with Barack Obama who he got to intervene on Brexit.

"I bet, and I can't prove it, that he made a desperate SOS call to Buckingham Palace to set that Sunday thing up... Andrew knew about it."

The SNP has called for the Queen to "remain steadfastly neutral" in a second independence referendum.

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SNP MP Tommy Sheppard told The Times: "This is shocking and extremely concerning.

"If true, it means that political pressure was applied to the Queen to press her into areas where the monarch should not go.

"I would hope that the palace would be able to give reassurance that the Queen will remain steadfastly neutral in the next referendum."