Scottish Secretary Alistair Carmichael should "question his whole approach to politics" if he thinks dirty tricks are a normal part of election campaigns, according to Nicola Sturgeon.

The Scottish First Minister was speaking in the wake of the leaking of a memo which claimed she would prefer David Cameron to be prime minister - an allegation Ms Sturgeon has described as ''100% untrue''.

Mr Carmichael earlier confirmed the memo, containing an account of a private meeting between First Minister Nicola Sturgeon and the French ambassador, was written in the Scotland Office.

The Liberal Democrat denied the leak was embarrassing for the Government department, stating "this is the middle of an election campaign, these things happen".

Responding to Mr Carmichael's comments, Ms Sturgeon said: "I think Alistair Carmichael really needs to question his whole approach to politics if he thinks dirty tricks and smear campaigns are just how things are done in elections.

"I take a very different view. I think elections should be a battle of positive ideas and that's how I'll continue to campaign."

Cabinet Secretary Sir Jeremy Heywood has ordered an inquiry into how the note - which claims that Ms Sturgeon told ambassador Sylvie Bermann that she would prefer to see Conservatives remain in power after the May 7 poll - got into the public domain.

Ms Sturgeon called for answers from the probe as soon as possible and insisted the allegation contained within the memo has been "completely answered".

She said: "I didn't say what I was alleged to have said. The French Ambassador has said I didn't say it, so that part of this story really has been dealt with and should no longer even be an issue.

"Now the questions are: who wrote this memo, how did it come to contain such an inaccuracy, but most importantly of all how did it very conveniently fall into the hands of the Daily Telegraph? I want answers to these questions and I want them as quickly as possible."

Ms Sturgeon was speaking on the campaign trail in East Dunbartonshire, where she visited a care home to launch the SNP's pensioners' plan to protect the interests of Scotland's older people.

She said: "I appreciate the SNP's challenging the Westminster establishment in this election.

"We're challenging the old boys' network and we're challenging that cosy consensus of Labour, the Liberals and the Tories who want more austerity cuts.

"So, I guess it's not surprising there are people in the Westminster establishment who don't like that message and who want to fight back against it, but I'll continue to take our positive message to the doorsteps, the streets, the communities of Scotland, because I believe it's the right one."

Mr Carmichael previously confirmed the memo was written in the Scotland Office during an interview with Channel 4 News.

Asked if the incident was embarrassing for him and for the Scotland Office, he replied: ''No, look this is the middle of an election campaign, these things happen.

"I understand that the memo in question did actually come from the Scotland Office, but these things are circulated within government."

The memo was written by a British civil servant following a conversation with consul-general Pierre-Alain Coffinier regarding a meeting between Ms Sturgeon and Ms Bermann, who was on her first visit to Scotland in February.

Earlier, deputy SNP leader Stewart Hosie insisted he could see Ed Miliband as prime minister because he leads the Labour Party.

Mr Hosie, MP for Dundee East in the last parliament, told BBC Radio 4's Today programme his party did not want a Tory government.

He said: ''We are an anti-Tory party, we are an anti-austerity party. We have offered Ed Miliband a deal.

''We would not prefer to see a Tory government. The damage Tory governments do to ordinary people is so bad.''

He was asked a number of times whether he thought Mr Miliband was prime minister material. Mr Hosie first responded: ''He is leader of the Labour Party and therefore he potentially could be prime minister.''

He later added: ''Of course one could see him as prime minister. He is leader of the Labour Party and therefore quite conceivably could be. Of course I could see him as prime minister.''

He also said he hoped there would be a large number of SNP MPs in the Commons after the election to keep Labour ''honest'' and ensure it does not continue with the Tory cuts.