Image copyright PA Image caption Alistair Carmichael is the only remaining Lib Dem MP in Scotland

Campaigners have begun a legal attempt to overturn the election of the former cabinet minister Alistair Carmichael as the MP for Orkney and Shetland.

The Lib Dem MP has faced calls to resign over the leak of a memo which suggested SNP leader Nicola Sturgeon wanted David Cameron as prime minister.

A petition was lodged at the Court of Session in Edinburgh in the name of four islanders.

They raised more than £40,000 through the internet to pay their legal costs.

The petition alleges that Mr Carmichael, Scotland's only remaining Lib Dem 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.

Can Alistair Carmichael's election be overturned?

Section 106 of the Representation of the People Act states that a person who "makes or publishes any false statement of fact in relation to the candidate's personal character or conduct shall be guilty of an illegal practice, unless he can show that he had reasonable grounds for believing, and did believe, that statement to be true".

Read more here.

It was presented to judge Lord Uist and will now be considered by the Election Court in what is believed to be the first case of its kind in Scotland for half a century.

The court heard that the petition would focus on "character" rather than "conduct".

"Today is the start of clearing the air which has become really poisonous in our islands," said Tim Morrison, one of the petitioners, outside the court in Edinburgh.

"We would like Alistair Carmichael to stand down," he said, adding that it should be up to the voters of Orkney and Shetland to decide whether or not to re-elect him in a by-election.

French Ambassador

Mr Morrison and his fellow campaigners allege that the electorate was misled because Mr Carmichael lied about his knowledge of a controversial memo about the SNP leader.

Last week, an official Cabinet Office inquiry found Mr Carmichael approved the leak of the memo, which was published at the start of the general election campaign on 3 April.

Image copyright other Image caption Ms Sturgeon tweeted Mr Carmichael's letter of apology

The document, written by a civil servant in the Scotland Office, claimed Scotland's first minister told the French Ambassador to the UK that she would prefer Mr Cameron as prime minister rather than Ed Miliband.

Both Ms Sturgeon and the ambassador insisted this was not the case, and the memo had contained a disclaimer that parts of the conversation may have been "lost in translation".

The Lib Dem MP wrote to Ms Sturgeon to apologise, saying the "publication was a serious breach of protocol and the details of that account are not correct".

At the time of the leak, Mr Carmichael had said he first heard of the memo when he was contacted by a journalist.

He has since acknowledged that while he had not seen the document before it was published, he was aware of its content and agreed that it should be made public.

Standards commissioner

Opponents said that if the truth about who leaked the memo had emerged during the general election campaign it could have altered the result in his constituency, where the former Secretary of State for Scotland was returned by a majority of just 817.

Tim Morrison said he was a member of the Scottish National Party but insisted the action was not politically motivated.

"I am here as a voter in my constituency," said Mr Morrison, 50, who flew from Kirkwall to Edinburgh on Friday morning and arrived at the court shortly after 15:00.

"We hope this process redeems the individual and the nature of politics in one go."

There have been protests on the islands calling for Mr Carmichael to stand down but he insists he will not, saying he has apologised, forfeited his ministerial pay-off and will continue as MP.

The parliamentary standards commissioner is considering whether to accept a complaint about his conduct. Police Scotland have also received a complaint.