NICOLA Sturgeon's success in the televised leadership debate has been overshadowed by a row over allegations the SNP leader told the French Ambassador to the UK she wanted David Cameron to remain in Downing Street after the General Election.

The First Minister, who had won a snap poll following Thursday's seven party debate, is alleged to have told Sylvie Bermann during their private meeting in February that she would 'rather see' the Tory leader win next month's General Election.

It was alleged by the Daily Telegraph, based on what it said was an official UK Government account of their conversation, that she did not regard Ed Miliband as 'prime minister material.'

Ms Sturgeon almost immediately issued a robust denial to her 154,000 followers on social media. In a broadside at the reporter who co-wrote the story she tweeted that it was "categorically, 100%, untrue...which I'd have told you if you'd asked me at any point today."

In a separate statement, a spokeswoman for the First Minister added: "As the First Minister has said, this story - which is based on a UK Government document - is categorically, 100 per cent untrue. It must be a belated April Fool.

"As Nicola has said on numerous occasions, she wants to see the back of a Tory government which is decisively rejected by the people of Scotland and unlike Labour, the SNP is the only party that had promised to lock David Cameron out of Downing Street."

The communique was reportedly typed up on March 6, and was said to have been based on a briefing to a senior civil servant and the French consul-general Pierre-Alain Coffinier about UK politics.

Mr Coffinier allegedly told a newspaper, after the allegations emerged, that Ms Sturgeon made no such claim.

The newspaper claimed the First Minister told Mr Coffinier: "The FM stating that she wouldn't want a formal coalition with Labour; that the SNP would almost certainly have a large number of seats... that she'd rather see David Cameron remain as PM (and didn't see Ed Miliband as PM material)."

The allegation surfaced at the end of a day which saw the Conservatives claim that the nationalists would form a "lethal cocktail" with Labour at Westminster.

The Tories also spliced together comments from Mr Miliband and Ms Sturgeon in a new video to suggest that ordinary people would suffer if they were in power together.

The SNP, with Ms Sturgeon in Edinburgh yesterday, said that their message of friendship to England had landed with a significant proportion of Labour and Lib Dem voters south of the border.

Both Labour and the Conservatives were forced to deny suggestions they would be forced into a deal with the SNP or Ukip, after neither party managed to deliver a killer blow in the TV showdown.

The Tory advert cuts from Ed Miliband saying: "If I'm Prime Minister" to a shot of the SNP leader saying "it will be ordinary people across the country who pay the price." It then cuts back to the Labour politician who says: "That's a clear promise from us".

Earlier the Conservatives had released a new poster depicting Ms Sturgeon as Prime Minister with Mr Miliband in her pocket.

Labour hit back at the Tories "lethal cocktail" jibe demanding David Cameron rule out the "poisonous proposition" of a deal with arch eurosceptics Ukip.

Labour focussed on previous support among some senior Ukip politicians for a privatised NHS.

Labour warned any deal with Nigel Farage's team could spell the end of the health service its current form.

Scotland has become a major battleground of contention between Labour and the Tories, in what has so far been an extremely tight battle for the keys to Downing Street.

Yesterday the Conservatives achieved their best poll rating in a year in a YouGov survey which put them on 37 per cent. However, Labour also coming close to their recent peak, and only just behind the Tories, on 35 per cent.

Edinburgh-born Tory Chief Whip Michael Gove warned that her party would pull Mr Miliband "well to the left" if he was forced to rely on their votes in the Commons.

"We saw in Nicola Sturgeon, certainly an impressive performance but also a performance from someone well to the left of not just the centre ground of British politics, but well to the left of Ed Miliband," he said.

"I think it is a leap that is unmerited by the polls to say that a SNP-Labour government would be a popular choice in this country," he added.

"I think that people appreciate that there would be an inherent instability in that arrangement.

"If the country chooses to it could vote for a patchwork coalition ... I prefer to say a lethal cocktail of different parties which all have different objectives - there would be an automatic instability."

An average of seven million viewers watched the TV debate.

One snap poll after the debate handed victory to Ms Sturgeon.

The SNP leader had told more than seven million viewers across the UK that she wanted to be "a voice to help bring about change for you too."

Labour's shadow energy secretary Caroline Flint accused the Tories of provoking anti-English feeling against the SNP, to boost the nationalists poll ratings in Scotland.

Many senior Labour figures, north and South of the border, argue that they are now caught in a pincer movement between the Conservatives on the one hand and the SNP on the other.

"(The Conservatives) would love Nicola Sturgeon to do well because that puts David Cameron back in No 10," Ms Flint said.

Meanwhile Mr Clegg launched a poster highlighting the tax cuts delivered by the Lib Dems in Hyde, Cheshire, which the party said was one of its manifesto promises delivered.

Today Labour will unveil a new poster warning that letting the stories back into power will cost every family £1,1000 because of George Osborne's plans.