Give Carmichael a second chance, pleads Rennie, as pressure grows for him to quit as MP

His support came as a petition calling for him to go attracted more than 10,000 names.

The SNP stepped up its effort to force him out, highlighting a local newspaper column from five years ago when the former Scottish Secretary wrote of the need for MPs "to tell the truth".

Mr Carmichael accepted responsibility for the leaking of a civil service memo which suggested Ms Sturgeon wanted David Cameron to win the General Election.

A Cabinet Office inquiry found he could and should have stopped the document being passed to a Conservative-supporting newspaper by his special adviser Euan Roddin.

The civil servant's memo recounted a conversation with Pierre-Alain Coffinier, the French consul-general in Edinburgh, in which the diplomat described a meeting between Ms Sturgeon and Sylvie Bermann, the French ambassador.

It was reported the First Minister told the ambassador she wanted Mr Cameron to remain prime minister, a claim categorically denied by both Ms Sturgeon and Ms Bermann.

The document was leaked despite the civil servant casting doubt on the reliability of Mr Coffinier's account, warning in his memo

of "something being lost in translation".

The potentially damaging claims emerged a month before the election when Ms Sturgeon was promising to "lock the Tories out" of office.

At the time Mr Carmichael insisted he had not seen the memo prior to its publication in the Daily Telegraph.

But following the damning Cabinet Office report he admitted he had sanctioned the leak, accepted the claims were inaccurate, apologised to Mr Sturgeon and Ms Bermann and forfeited his ministerial severance pay of £17,000.

He acknowledged he would have had to resign as Secretary of State, had he still been in the job, but signalled his intention to remain MP for Orkney and Shetland, where his majority was slashed to a wafer-thin 800 votes.

As pressure mounted on him to go, Mr Rennie said in a statement he had discussed the "serious nature" of the leak with Mr Carmichael who regretted it and "fully understands the impact it has had on his reputation."

The MSP added: "I have known Alistair for almost 30 years and have worked closely with him in parliament for almost a decade.

"I have always been impressed by his energy, dedication and professionalism.

"He has served Orkney and Shetland for 14 years and has been elected on four separate occasions. "It is clear to me that recent events are an aberration."

The Scottish Lib Dem executive, the party's ruling body, gave Mr Carmichael its backing at a meeting on Saturday, Mr Rennie said.

He pleaded: "As a liberal I believe that people deserve a second chance. "I hope fair minded people would agree that Alistair Carmichael should be given that second chance.

The SNP helped to organised a protest in Lerwick on Saturday that was attended by about 50 people.

SNP members also urged people to sign an online petition calling for him to go.

Referring to a column by the MP in the Shetland Times, Mike McKenzie, an SNP Highland and Island MSP said: "Just when Mr Carmichael thought things couldn't get any worse he has been caught in breach of his own code - and this further deepens the credibility crisis he now finds himself in.

"Mr Carmichael's newspaper column in the Shetland Times, where he cites the dangers of political smears and the need for MPs to be truthful - along with his support for the right of constituents to recall their MP - leaves his position increasingly perilous."

He added: "Mr Carmichael misled his constituents during an election, and the only way that he can relieve the pressure he is under is to stand down.

"Had Alistair Carmichael admitted the truth before polling day, he would have been a discredited candidate and the result may well have been different. It's possible he would have gone the same way as every other Lib Dem MP in Scotland and been turfed out by the voters."