David Cameron has said he fully backed an inquiry into how a private UK Government memo involving First Minister Nicola Sturgeon got into the public domain.
The prime minister said it was “not acceptable behaviour” to leak documents and wanted to know who was responsible.
The leaked document claimed Ms Sturgeon would prefer the Conservative MP Cameron as prime minister over Labour leader Ed Miliband, but she branded it “100% untrue”.
Cabinet Secretary Sir Jeremy Heywood has ordered an inquiry into how the note – which reported the disputed details of a discussion between Ms Sturgeon and French ambassador Sylvie Bermann – got into the public domain.
Scottish Secretary Alistair Carmichael, a Liberal Democrat, has confirmed the memo was written in the Scotland Office but claimed “this is the middle of an election campaign, these things happen”.
Asked if he believed the SNP leader said she wanted him to continue to be prime minister, Mr Cameron said: “I do not know, I did not see this document.
“I abhor the leaking of documents, we need to be able to have private diplomatic conversations.
“I see, as prime minister, everyday the importance of that protocol.
“So there is a proper leak inquiry going on.
“This is not acceptable behaviour and I want to get to the bottom of who did this.”
Mr Cameron said it was wrong that Mr Miliband appeared prepared to ride into Downing Street on the “coattails” of the SNP which is hoping to hold the balance of power in a hung parliament.
“My view for the last four years is that Ed Miliband is not up to the job of being prime minister and I am always delighted when anyone joins me in that widely held opinion,” added the prime minister.
Andy Birnham, a member of Mr Miliband’s shadow cabinet, claimed the party owed Ms Sturgeon no apology over its reaction “in good faith” to the leaked memo, which was written by a civil servant.
Muhammad Shoaib, an organiser of the Asians for Independence campaign, has quit the SNP because he believes senior party figures do secretly back a Tory election victory.
The 62-year-old from Glasgow has joined the Scottish Labour Party.