Yesterday's vote on tuition fees  was the Liberal Democrats' Iraq moment, a profound breach of trust for which the party will pay dearly at the next election. In little more than eight months, the Lib Dems have fallen from 34 per cent in the polls to just 8 per cent , their lowest rating for 20 years. They are certain to lose votes and seats at the next election. But who would benefit most from a Lib Dem meltdown?
It is the Conservatives who stand to win the most seats off Nick Clegg's party. The Tories are currently in second place in 39 of the Lib Dems' 57 seats, typically by a considerable margin. By contrast, Labour is in second place in just 16.
As UK Polling Report shows, while 13 of the Tories' top 50 target seats  are Lib Dem-held, just six of Labour's  are. A poll of marginals  by the Conservative Party deputy chairman Michael Ashcroft in July suggested that the Tories can hope to win as many as 30 seats off the Lib Dems.
But Labour supporters can derive much comfort from the fact that a wave of Lib Dem defectors will allow them to win back dozens of seats from the Conservatives. As a Fabian Society analysis  pointed out earlier this year, there are 25 seats that would swing back from the Conservatives to Labour if just one in five Lib Dem voters switched to the red team.
In addition, a defection of this size would allow Labour to win 15 seats off the Lib Dems, including all five gains that Clegg's party made at the last election – Norwich South, Bradford East, Brent Central, Burnley and Redcar. Encouragingly for Ed Miliband, a recent ComRes/Independent  poll found that more than one in five people who voted for the Lib Dems say they would now vote Labour.
But the risk for Labour is that justifiable anger at the Lib Dems unwittingly allows the Tories to avoid the blame for unpopular decisions. As Ed Balls points out  in his latest Tribune column:
The Prime Minister plays the global statesman – travelling around the world and hosting foreign leaders in Downing Street – but rarely allows himself to be dragged into domestic policy controversies. George Osborne is rarely seen in public defending his reckless gamble with the economy.
But week after week it is Lib Dem ministers like Danny Alexander and Vince Cable who find themselves in TV studios defending what are essentially Conservative policies in a predominantly Conservative government. The Lib Dems have willingly become David Cameron's human shields, haemorrhaging support in the process.
Unless Labour begins to develop a more coherent critique of the Conservatives, Cameron's party, not least under the redrawn constituency boundaries , could be in a strong position come the election.