Nicola Sturgeon: Q&A on the civil service memo row that eclipsed the leaders' debate

Who benefits from this leak?

Nicola Sturgeon (Ken McKay/ITV/PA)

Is the leaked letter genuine?

The Foreign Office said they searched their files, and were "not aware of such a document". Translation: it’s not a fake. The Scotland Office are not so certain.

Their senior ranks said the letter was not a forgery, and it was "eminently possible" it came from them. Translation: the Telegraph’s description of the leaker as a "senior British civil servant" disguised its origins. The French consul did not say the election wasn't discussed, only that Ms Sturgeon had not revealed her "preference" on the outcome.

What does Sturgeon's office say?

The story, she says, is "categorically 100 per cent, untrue". Although stopping short of shouting "conspiracy" Scotland's First Minister called Whitehall "out of control" and a place where "political dirty tricks are manufactured". She called on the head of the UK Civil Service, Sir Jeremy Heywood, to carry out an urgent inquiry of the "false account".

Who benefits from this leak?

Lots of people, arguably. At first glance it damages the SNP, and contradicts their demand to be part of a "progressive alliance" that locks David Cameron out of Number 10. That doesn't square with wanting five more Tory years.

Allegations of a unionist "conspiracy" that manufactures lies? That confirms what many nationalists already believe. The SNP as innocent victims of the UK playing dirty is a narrative they will positively use.

Ed Miliband called the leak "damning" and Jim Murphy, the Scottish Labour leader, called it a "devastating revelation".

The Scottish LibDems said "Now we know what she [Sturgeon] really thinks", and the Tories, obviously, were happy Sturgeon was backing Cameron. So all the main parties have already started using what it says.

Why do people say Sturgeon wants a Tory win?

The SNP has remained relatively blame-free in Holyrood. They continue to point the finger at Westminster for any perceived funding failures, with any achievements solely of their making. Signing up to a Labour-led project risks that track record.

If a Miliband administration got into trouble, any SNP "agreement", however loose, could risk blame coming their way. And if there was no trouble? Well, no need for separation then - because the UK works.

Another five years of the Conservatives is different. Cameron wants an ‘English votes for English laws' (EVEL) system. That could leave Scottish MPs as second class members in the Commons.

And if, as forecast, the SNP sends record numbers to Westminster, Scotland begins to look like suffering from a democratic deficiency – an unrepresented colony in other words. That brings the prospect of a second referendum far closer.

A lot of people might have liked to leak it but how many people actually get to see such memos?

The FCO can sit in on ambassadorial meetings, but didn’t on this one. All ministers in the Scotland Office are routinely sent memos of consular meetings in Edinburgh. Scotland Office officials often produce accounts of such meetings, and the memos can go to both the Scotland Office and the Foreign Office in London.

This time, the FCO say nothing went south. Alistair Carmichael, the Lib Dem Scottish Secretary, says he knew nothing of the leaked memo till his officials warned him of the Telegraph story.

Does the civil service normally leak stuff?

Leaks of diplomatic chit-chat are highly unusual. Records of discussions between leading UK politicians and ambassadors are well protected.

How many people have ever been caught by a government leak enquiry?

Precious few. The general rule is that if Whitehall wants to find someone badly enough, they will. The question is, do they?

Is there any significance that this has appeared in the Telegraph? Didn’t the Telegraph carry the letter from those business people? Or is it simply a good story?

As Francis Urquhart, the Prime Minister in Michael Dobbs' original House of Cards, often remarked: "You may say that, I couldn't possibly comment."