Douglas Alexander said instead of thinking about a deal with Nick Clegg's party, Labour should expose them as "enablers" of Tory cuts.
The Renfrewshire MP and shadow foreign secretary said the cost-of-living crisis - with the average family £1600 worse off than in 2010 - would be the defining question in a "winnable General Election".
Reminding delegates at the Scottish Labour conference that the Tories hadn't won a Westminster majority since 1992, he said: "It's not just that they have one Tory MP in Scotland, they don't have a single elected councillor in the great cities of Liverpool, Manchester, Sheffield or Newcastle.
He said Tory Party membership had halved under David Cameron, while Clegg and his MPs "voted for the bedroom tax, voted to triple tuition fees, and have got it wrong on the economy.
"Anybody who suggests we should try and have a coalition with them, it's nonsense. We will deliver a majority Labour government."