The Conservatives dramatically stepped up their rhetoric against Nicola Sturgeon after the televised leaders' debate, claiming the Nationalists would form a "lethal cocktail" with Labour at Westminster.

The Tories wasted no time in launching a new attack video on the SNP leader following Ms Sturgeon's widely praised performance in Thursday's seven party ITV debate.

It spliced together comments from Mr Miliband and the First Minister to suggest that ordinary people would suffer if they were in power together.

The Conservatives are keen to build on concerns about the potential sway the SNP could have on a Labour Westminster administration after the General Election on May 7.

The party warned the effect could be to destabilise the country and undermine the economic recovery.

Edinburgh-born Tory chief whip Michael Gove said: "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."

Labour hit back, demanding Prime Minister David Cameron rule out the "poisonous proposition" of a deal with arch eurosceptics Ukip.

Meanwhile, the SNP said that their message of friendship to England, in a programme watched by more than seven million people, had resonated with a significant proportion of Labour and Liberal Democrat voters.

As Ms Sturgeon campaigned in Edinburgh, the SNP claimed more than 2000 people had joined the party since the debate.

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 poster depicting Ms Sturgeon as Prime Minister with Mr Miliband in her pocket.

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 are only just behind, on 35 per cent.

South of the border Mr 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."

A YouGov snap post-debate poll handed victory to Ms Sturgeon.

The SNP leader had told viewers 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.

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.