Image copyright Dan Kitwood/Getty Image caption Alistair Carmichael formerly served as Scottish Secretary in the coalition government

The Parliamentary Standards Commissioner has launched a formal inquiry into the conduct of former Scottish Secretary Alistair Carmichael.

The Orkney and Shetland MP has been under pressure after admitting the leak of a memo during the election campaign.

The memo had suggested First Minister Nicola Sturgeon would prefer David Cameron as prime minister.

The watchdog will consider Mr Carmichael's actions under the MPs' code of conduct.

The confidential memo at the centre of the controversy was written by a civil servant in the Scotland Office.

It was a third-hand account of a conversation between the Scottish first minister and the French ambassador, in which Ms Sturgeon was reported to have said she wanted David Cameron to remain as prime minister.

Code of Conduct

The Parliamentary Standards Commissioner will investigate Mr Carmichael's actions under three sections of the MPs' code of conduct. These are:

Section 10: Members shall base their conduct on a consideration of the public interest, avoid conflict between personal interest and the public interest and resolve any conflict between the two, at once, and in favour of the public interest.

Section 14: Information which members receive in confidence in the course of their parliamentary duties should be used only in connection with those duties. Such information must never be used for the purpose of financial gain.

Section 16: Members shall never undertake any action which would cause significant damage to the reputation and integrity of the House of Commons as a whole, or of its members generally.

Both the first minister 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 official cabinet office inquiry into the leak said Mr Carmichael's former special adviser Euan Roddin gave the details to the Daily Telegraph - but that he had Mr Carmichael's permission to do so.

Mr Carmichael had denied knowing about the memo when asked about the leak at the time, saying the first he had heard of it was when he received a phone call from a journalist.

He has since apologised and accepted full responsibility for the leak.

The SNP have said that Mr Carmichael faced a "credibility crisis", and repeatedly called for a formal investigation by the Parliamentary Standards Commissioner to be held.

Mr Carmichael has previously rejected calls to resign, saying that his work as a local MP is "the record on which I am entitled to rely."

"That's the job that I am now going to be getting on with. None of that has changed," he has said.