Cover-up fears grow as Cabinet Office refuses to reveal date of Frenchgate confessions

The leak incensed Sturgeon, who vehemently denied saying she wanted Cameron to remain in power during a meeting with French Ambassador Sylvie Bermann.

On April 4, the UK Cabinet Secretary Sir Jeremy Heywood instigated "a Cabinet Office-led leak inquiry to establish how extracts from this document" got into the Daily Telegraph.

However it was not until May 22, seven weeks later, that the inquiry's conclusions were finally published, and Carmichael and Roddin named as the culprits.

The timing fuelled suspicions there had been a politically motivated delay to make sure nothing embarrassing was revealed until after the election.

When the inquiry was set up, the Tories were unsure if they would need the help of the LibDems to form a second coalition and so had reason to protect Carmichael.

After May 7, however, a superfluous Carmichael was duly named and shamed.

Having initially denied all knowledge of the leak, he is now the subject of a court action by four constituents trying to have his election as MP for Orkney & Shetland declared void.

Using Freedom of Information law, the Sunday Herald asked the Cabinet Office for the date on which Roddin first confirmed he leaked the memo, the date the inquiry concluded Roddin and Carmichael were to blame, and the dates on which the pair accepted the findings.

This would show if the key facts were known before the election and withheld from the public.

The Cabinet Office refused to release the dates on the grounds they "would assist a person to avoid detection in the future" and "seriously impact on future investigations".

The Sunday Herald has challenged the decision.

The Cabinet Office has used the same excuse not to reveal who else in the UK government got the memo - however the Scotland Office has used a different excuse for withholding the same information, namely that it could damage people's "physical and mental health".

The Scotland Office has also refused to release the full memo on the grounds it could damage Anglo-French relations, despite almost all the text being public already.

The growing list of FoI refusals has prompted claims of a cover-up.

SNP MP Peter Grant, who has tabled a Commons motion deploring the "spurious reasons" for secrecy, said: "The reasons being used by the UK government to keep covering up basic information about this leak are getting more nonsensical and harder to sustain.

"The information requested is specific to this case, and these blanket refusals based on what might or might not occur in the future are clearly stonewalling exercises.

"It is very important to know precisely when the truth was established, both in terms of the wider public interest and also because that information will presumably be relevant to the electoral court case being heard against Alistair Carmichael - which hinges on untrue statements being made by him before the election.

"Knowing whether or not it was established by the inquiry prior to the election that his statements were inaccurate is a key aspect."

Alex Salmond has claimed David Mundell, Carmichael's Tory deputy at the Scotland Office before the election and now the Scottish Secretary, "must have seen the infamous memo".

The Frenchgate memo was written on March 6 by a Scotland Office civil servant after a phone call with the French Consul General in Edinburgh about the Sturgeon-Bermann meeting.

The memo writer said that, according to the Consul General, Sturgeon "confessed that she'd rather see David Cameron remain as PM (and didn't see Ed Miliband as PM material)".

However the civil servant also doubted "the FM's tongue would be quite so loose" and warned "it might well be a case of something being lost in translation".

Despite the problems, Roddin urged the memo be leaked and Carmichael agreed.