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.
Nicola Sturgeon has said people across the UK will not forgive Ed Miliband if he turns down the chance to lock the Conservatives out of Downing Street.
Speaking on the campaign trail in Ayrshire today, Sturgeon said: "If there is an anti-Tory majority in the House of Commons after the election, then the only way David Cameron gets back into Downing Street is if Ed Miliband stands back and lets him back into Downing Street.
"If Ed Miliband and Labour do that, they will not be forgiven, certainly in Scotland and I suspect in large parts of the UK as well."
"It was very clear last night that on its own, Labour is not going to be bold enough to offer a real alternative to the Tories," she added.
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.