ALISTAIR Carmichael, the Scottish Secretary, has called on Alex Salmond to stem the cybernat "poison", which he warns is threatening to debase the referendum debate.

Last night, a spokesman for the First Minister said the denigration of people had "absolutely no place in the referendum debate", whichever side it came from.

The issue of the tone of the campaign was raised at Scottish Questions in the Commons by Margaret Curran, Labour's shadow Scottish secretary, who said all businesses had a right to be heard without fear of insult or intimidation.

Mr Carmichael responded by referring to the "poison" that was entering the independence debate from "cyber-interventions".

Stressing how Scots would have to work together whoever won the September poll, the Secretary of State said: "That is not going to be possible if we allow the well to be poisoned in the way the cybernats in particular seemed determined to do."

Ms Curran said she had been told by business leaders of "intimidatory tactics" used to stop them intervening in the debate and mentioned how Bob Dudley, the BP boss, who this week called for the UK to stay together, had been dismissed by the Yes campaign as a British Nationalist.

Later, the Scottish Secretary said: "Frankly, unless the political leadership of all parties on all sides get a grip, it could become a problem. Most significantly, it could act to discourage people who are not politicians and not public figures from entering the debate," he explained.

Asked if he felt the main culprits of intimidation were on the Nationalist side, Mr Carmichael said: "I know of nobody suggesting that anybody on the pro-UK side of the debate has acted in that way." Asked if his appeal not to allow the "poison" to debase the debate was largely directed at the SNP, he replied: "The Nationalists, yes."

A spokesman for the First Minister said: "Denigration of people has absolutely no place in the referendum debate, it doesn't matter whether those doing it support Yes or No."

He pointed out how: Nicola Sturgeon had received death threats on Twitter; a posting on the No campaign's Facebook page talked about firing bullets into SNP leaders; appalling remarks about Mr Salmond's father were made on a Labour Party website and this week a man appeared in court charged with posting a message on Twitter threatening to kill the FM.