Image copyright PA Image caption A judge ruled that Mr Carmichael had told a "blatant lie" about his involvement in the leak

An investigation into the involvement of former Scottish secretary Alistair Carmichael in a leak aimed at damaging Nicola Sturgeon has been dropped.

The memo suggested Ms Sturgeon had told the French ambassador she would prefer David Cameron's Conservatives to win the 2015 general election.

Ms Sturgeon denied the claim, and the Parliamentary Commissioner for Standards was asked to investigate.

The commissioner has now said it falls outside her remit.

This was because Mr Carmichael had been made aware of the memo through official Scottish Office channels, and not due to his role as an MP.

The commissioner, Kathryn Hudson, said: "I have established that the conduct which led to my inquiry falls outside my remit. I do not, therefore, make any criticism, or indeed any other comment, on Mr Carmichael's conduct in this affair."

'Investigative report'

Responding to the commissioner's report, Mr Carmichael said: "I am pleased that this is now resolved and will continue to focus on getting on with my job as MP for Orkney and Shetland."

Ms Hudson said she did not have sufficient information from the Cabinet Office to be able to answer questions about Mr Carmichael's role in the matter at the beginning of her inquiry.

She added: "On the same day that I initiated my inquiry, I wrote to the Cabinet Secretary to ask if he might release to me a full copy of the report of the leak inquiry carried out by Cabinet Office officials.

"On June 16 2015, the Cabinet Secretary told me that he did not think it would be appropriate to release a copy of the investigative report."

The commissioner also used her report into the matter to suggest that a review of the code of conduct for MPs should look at whether members seeking re-election should continue not to be covered by its rules during the period of a general election campaign.

Both Ms Sturgeon and the French ambassador insisted she had not made the comments contained in the Scotland Office memo, which was obtained by the Daily Telegraph newspaper ahead of last year's general election.

Legal action

The memo had contained a disclaimer that parts of the conversation between the Scottish first minister and the ambassador may have been "lost in translation".

Mr Carmichael claimed in a Channel 4 TV interview at the time that the first he had heard of the leak was when he received a phone call from a journalist.

He had in fact authorised his special advisor to leak the memo, an action he admitted days after being elected as the MP for Orkney and Shetland.

Four of his constituents launched a legal action aimed at having his election overturned, claiming he misled voters over the memo.

But judges ruled in December that it had not been proven beyond reasonable doubt Mr Carmichael had committed an "illegal practice".

However, judge Lady Paton said in the ruling that Mr Carmichael had told a "blatant lie" in the Channel 4 interview.