Ed Miliband and Nicola Sturgeon are "at the altar, and preparing to sign the register" on a post-election deal, according to Scottish Conservative leader Ruth Davidson.
Sturgeon made the Labour leader an offer to join forces to help him become Prime Minister during the TV debates.
But David Cameron has warned there would be more borrowing and higher taxes if Miliband goes ahead with the deal.
When asked again today whether Labour would enter a formal coalition with the Scottish Nationalists to form a government, Ed Miliband repeated that it wouldn't happen.
However, the Labour leader did stop short of ruling out some sort of post-election pact, should his party fail to win a majority.
Meanwhile, SNP leader Nicola Sturgeon repeated her call for Labour to join forces, saying that only together could they lock the Tories out of Downing Street.
ITV News Deputy Political Editor Chris Ship reports:
The Ukip leader said he did not "lose my rag" when he attacked the audience during last night's televised debate for their "left-wing bias."
We watched undecided voters as they watched the debate hoping it might help them make up their minds.
Ed Miliband appeared to turn down Nicola Sturgeon's latest offer as the leaders of five "challenger" parties took part in a heated debate.