Claims of bullying have emerged as the vote draws near, with a series of emails between Alex Salmond's special adviser and the principal of St Andrews University published in the Daily Telegraph.

The correspondence, dated March last year, shows the adviser offering a prepared statement for principal Louise Richardson to speak of her confidence in the Scottish government's ability to maintain research council funding for universities.

It came after an interview Ms Richardson gave to The Times newspaper in which she expressed concern and described as "catastrophic" the consequences if those funds were no longer available in the event of independence.

A spokesman for Mr Salmond told the Telegraph the emails were part of "routine dialogue" and said all discussions were "cordial".

In an interview with The Times Prime Minister David Cameron said he was "disturbed" by allegations of intimidation.

Yesterday Labour leader Ed Miliband claimed the campaign for independence has an "ugly side" following chaotic scenes when he was mobbed during a visit to Edinburgh.

Yes Scotland has previously said it condemns all forms of abusive, dangerous and offensive behaviour.