THE Liberal Democrats have launched a desperate rearguard action to save Alistair Carmichael, their sole Scottish MP, in the face of growing pressure for him to resign his seat.

Willie Rennie, the Scottish LibDem leader, publicly backed the beleaguered Orkney and Shetland MP, describing his role in a bid to smear Nicola Sturgeon as "an aberration" and called for him to be given a second chance.

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.

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

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."

The Scottish LibDem 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 hope fair minded people would agree that Alistair Carmichael should be given that second chance.

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."