Media playback is unsupported on your device Media caption Nicola Sturgeon "absolutely, 100%, categorically" denies claims she said she would prefer a Tory government

SNP leader Nicola Sturgeon has accused Whitehall of "dirty tricks" after a report emerged claiming she told a French diplomat she would prefer David Cameron in No 10 over Ed Miliband.

The Daily Telegraph published a memo claiming Scotland's first minister privately said she would prefer David Cameron in No 10 over Ed Miliband.

Ms Sturgeon has said the story was "categorically, 100% untrue".

Cabinet Secretary Sir Jeremy Heywood said a leak inquiry had been set up.

In a letter to Ms Sturgeon he said: "You have asked me to investigate issues relating to the apparent leak of a Scotland Office memo that forms the basis of this morning's Daily Telegraph story.

"I can confirm that earlier today I instigated a Cabinet Office-led leak inquiry to establish how extracts from this document may have got into the public domain."

French officials said Ms Sturgeon did not express a preference for PM.

But Labour called the report "damning" and said that even if it was not true the "SNP are happy to see another Tory government".

Conservative leader David Cameron warned against a "coalition of chaos" between Labour and the SNP.

In other general election campaign news:

Ed Miliband unveiled a Labour plan to encourage banks to fund 125,000 new homes for first time-buyers in England

Culture Secretary Sajid Javid outlined Conservative plans to protect children from online hard-core pornography

The Lib Dems have unveiled plans for a £2.5bn care fund to help keep people out of hospitals through improved GP access, a wider range of services in doctors' surgeries and better healthcare in nursing homes

The Daily Telegraph published on its website a transcript of what it says is an official British government memorandum which includes details of a private meeting between Ms Sturgeon and Sylvie Bermann, the French Ambassador to the UK.

Included in a civil servant's summary is the line that Ms Sturgeon would "rather see David Cameron remain as PM (and didn't see Ed Miliband as PM material)".

'Completely false'

Ms Sturgeon said: "The real issue is how a second hand and inaccurate account of this meeting - which was not even attended by the UK government - came to be written by a UK Government civil servant and then leaked to Tory-supporting newspapers at the start of a general election campaign.

"It suggests a Whitehall system out of control - a place where political dirty tricks are manufactured and leaked. And the Foreign Office now appears to be denying the very existence of such a document."

The French consul general in Edinburgh, Pierre-Alain Coffinier, whose comments are claimed to have been the basis for the leaked memo, has told the BBC Ms Sturgeon did not express any preference for a leader.

Media playback is unsupported on your device Media caption French consul general in Edinburgh, Pierre-Alain Coffinier: "This is not an accurate report"

A spokesman for the French ambassador Sylvie Bermann, whose conversation with Ms Sturgeon was being briefed on in the memo, also said the SNP leader had not expressed an opinion on who she would prefer as prime minister.

A Foreign Office spokeswoman said they had no record of the memo. The Scotland Office said they did not comment on leaks.

'Damning revelations'

Polls suggest Ms Sturgeon's party could win a number of seats from Labour on 7 May.

Both the SNP and Labour have ruled out a formal coalition in the event of a hung Parliament.

But Ms Sturgeon has hinted at offering informal support to Ed Miliband in return for steering Labour away from "implementing Tory policies" on austerity.

She has ruled out a deal of any sort with the Conservatives, who have claimed that Ed Miliband wants to get in to No 10 "on the coat-tails" of the SNP.

Labour leader Mr Miliband has warned wavering supporters in Scotland that if they vote SNP they risk handing power to the Tories, because they could end up as the biggest party in Westminster and therefore get the first chance to form a coalition.

Media playback is unsupported on your device Media caption Ed Miliband: "These are damning revelations"

He said on Saturday that the claims about his party's biggest rivals in Scotland, reported in the Telegraph, were "damning revelations".

He said: "What it shows is that while in public the SNP is saying they don't want to see a Conservative government, in private they are actually saying they do want a Conservative government."

A Labour spokesperson added: "No one will ever know for certain what went on between Nicola Sturgeon and the French Ambassador. But what we do know is that the Tories are desperate for the SNP to do well, and the SNP are happy to see another Tory government."

David Cameron, campaigning in Abingdon, said: "What's Nicola Sturgeon told us today? Well she's told us - she's being anointed as this great genius - she's told us something that I said about four years ago, which is Ed Miliband is not up to the job of being prime minister. I think we knew that already."

The Green Party said there were "serious questions" about the leak.

"This is damaging to the reputation of our politically independent civil service and should be investigated as a matter of urgency," it added.