ALISTAIR Carmichael will have to fight off a legal challenge if he is to survive as an MP after a petition was lodged at Scotland's highest civil court aiming to have his narrow general election victory quashed.

The former Secretary of State for Scotland, who has come under pressure to quit after admitting responsibility for a leaked memo which wrongly suggested that First Minister Nicola Sturgeon wanted David Cameron to win the general election, will now be formally informed of the action.

Campaigners have raised more than £43,000 with an online fundraising drive in a matter of days allowing them to take their case to court. Almost 3,000 people donated an average of £15 each.

The petition alleges that the Liberal Democrat MP breached Section 106 of the Representation of the People Act 1983, which outlaws false statements in relation to the "personal character or conduct" of a candidate. It is understood it is the first such case to come before the Scottish courts since 1965.

Tim Morrison, an Orkney resident who is one of four petitioners, said the move was the start of "clearing the air which has become really poisonous in our islands".

However, while the legal bid will increase pressure on Mr Carmichael politically by ensuring high-profile media coverage, experts warned that it is highly unlikely to succeed.

Cabinet Secretary Sir Jeremy Heywood ordered an inquiry after the memo, which claimed Ms Sturgeon told French ambassador Sylvie Bermann that she would prefer to see Conservatives remain in power, became public.

Mr Carmichael, who had initially publicly claimed that he knew nothing about the leak, apologised after the Cabinet Office investigation concluded he ''could and should have stopped the sharing of the memo''. It was found that he had given authorisation to an advisor to pass it to a newspaper.

His opponents argue that had voters in his constituency known about his actions, he would have been unlikely to retain the seat he has held since 2001. The SNP narrowly avoided taking the seat, with Mr Carmichael winning a majority of only 817.

Mr Morrison, a member of the SNP, added: "Everyone has an opinion on what happened and what Mr Carmichael has done or not done, but we ordinary voters want to have our say now that we are in full possession of the facts.

"Mr Carmichael has apologised to us, his constituents. It's up to us to forgive him if we choose to in the ballot box. This should happen as soon as possible and certainly not in five years.

"We would like Alistair Carmichael to stand down, that's clear from this process, but we want him to stand down so that if he wants it, if the courts consider him fit, he can have the second chance. But it's up to us, the people, to give it to him."

Mr Morrison was present at court, where the petition was formally presented by Jonathan Mitchell QC at a hearing before Lord Uist. The judge made an order for Mr Carmichael to be formally notified of the petition.

Speaking outside the court, Robert Holland, partner at solicitors Balfour and Manson, said: "An election petition has been lodged today at the Court of Session.

"It has been accepted by the court and warrant has been granted for service. As far as the legal proceedings go it will take its usual course."

Professor James Chalmers, Regius Professor of Law at the University of Glasgow, said that the chance of success were "very unlikely but not impossible".

He said: "The petitioners are trying to use the law for something it was never designed for to do something that's never been done. They've got an argument to make, but I wouldn't want to bet any money on it succeeding."

Under the law, Professor Chalmers said they will have to show that Mr Carmichael made a false statement of fact about the leaked memo. They will then seek to prove it referred to a candidate - namely the MP himself which would require a broad interpretation of the law.

Then, they will seek to show that the statement was about the candidate's "personal character or conduct" which is not straightforward given the distinction between personal and political conduct.

Finally, they will seek to show that the statement was "for the purpose of affecting the return of any candidate at the election". Mr Carmichael may argue that the statement denying knowledge of the leak was not directly about the Orkney and Shetland vote, according to Professor Chalmers' analysis.

Aileen McHarg, Professor of Public Law at the University of Strathclyde: "I wouldn't put any money on it succeeding. I would think it's pretty much a non-starter, although it's always open to a different argument.

"The Act is very much focussed on regulating individual constituency campaigns, and the law has always drawn a distinction between national and constituency campaigns.

"It seems to me that what Alistair Carmichael did was focussed on the national campaign, rather than his own election. It was to attack the SNP generally, and improving the position of his party. There isn't a huge amount of contemporary case law, but the court is likely to draw that distinction.

"What he did may well have had an impact on his own chances of election, but that wasn't its primary purpose. It was about the national party, rather than any particular candidate."