The SNP have hailed poll results they say show Nicola Sturgeon's message of solidarity in the televised leaders' debates resonated with key voters south of the border.
The First Minister appealed directly to people outside Scotland to let the SNP be their "allies" in the fight against NHS privatisation.
Her call focused on one of the most controversial aspects of the SNP's election campaign so far.
There was uproar in England when the SNP leader announced plans to overturn long-standing party policy to abstain on issues to do with the English health service.
Her change of heart immediately prompted accusations that SNP MPs wanted to meddle in affairs that would not affect their constituents and led to renewed calls for 'English votes for English laws'.
For her part Ms Sturgeon defended the move, saying that as part of the UK many health issues, including cuts to overall NHS spending, would have direct knock on effects on Scotland.
But the SNP suggested the message of alliance over the NHS she delivered on Thursday night appealed to some voters.
The party said that analysis of a YouGov poll, which also judged the SNP leader the victor on Thursday night, showed she appealed to both Labour and Lib Dem voters.
It found that across the UK 33 per cent of Labour voters and 32 per cent of Lib Dem voters thought that Nicola Sturgeon had performed best on the night.
While YouGov gave Ms Sturgeon a clear victory other polls were less clear cut with a number suggesting little between the SNP leader, Mr Cameron, Mr Miliband and Ukip leader Nigel Farage.
The mixed picture - repeated in voting intention opinion polls which show both Labour and the Tories struggling to establish any kind of lead - points to why the Tories are also keen to win over wider UK public opinion on the SNP.
And they also appear to be able to claim some success.
Pollsters say that concern about the potential influence of the SNP after May are now starting to be mentioned in focus groups of voters in England.
However, while the SNP leader wants to appeal to left of centre voters concerned about issues such as the impact of the private sector on the health service, the Tories are focusing on shoring up their core vote.
The party hopes that potential Conservative supporters who are considering giving their vote to other parties could be brought back into the fold by claims of a "chaotic" SNP- Labour alliance.
The debate also saw Ukip leader Nigel Farage attempt to shore up his party's core vote, in the face of falling opinion poll ratings, with an attack on the SNP, but more generally the system of how Whitehall spending is allocated to Scotland, the Barnett formula.
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