He argued for the need to “change the way the economy works” and whom it works for. This found an echo in public opinion: Many feel that business has become less a means of generating wealth, fairly distributed, than a vehicle for personal enrichment, especially for some extraordinarily well-paid beneficiaries in the financial sector. Mr. Miliband’s proposal was to pile taxes on the rich, but this is not the same as making the needy better off or rewarding aspirational voters.

In the absence of any realistic program to reform the economy in a redistributive way, Labour fell back on a series of expensive financial offers to the public: capped energy prices and rail fares, controlled housing rents, a government-backed “living wage” and reduced tuition fees. Though welcome to many, these sounded implausible or unaffordable in straightened fiscal times.

This perception meshed with Labour’s reputation — largely, but not entirely, unmerited — for losing control of government finances when in office before 2010. Conservative strategists hammered home the message that Labour’s policies would bring chaos. Unfortunately, Mr. Miliband had failed to establish his fiscal credentials earlier; by the time of the election campaign, it was too late.

So what are the lessons from Labour’s electoral meltdown?

For a start, a party committed to radical change has to be careful in balancing its message. It needs to construct a case for change, not rely on sound bites. The “haves” in society are prepared to make sacrifices for the have-nots, but they need to be treated to a reasoned argument, not a “them and us” assault that undermines rather than builds consensus.

While people admire Labour and its commitment to social justice, they won’t sign up for what looks like an ideological vendetta, particularly if they fear becoming undeserving financial casualties of it. Voters are justly cautious.

There is no reason to believe they will always reject a leader to the left of Mr. Blair, but they do not regard business, big or small, as the enemy — much as they’d prefer to see business earnings properly tied to performance. If a political leader goes in for leftist rhetoric, they want it backed by a practical program. Otherwise, the message appears unhitched from reality.

In this election, the number of people undecided late in the race was greater than usual. I do not accept the idea that the pollsters were wrong because they simply underestimated so-called shy Tory voters. British elections are won in the center ground inhabited by a good 15 percent of the population who do not necessarily lean left or right. Those people want to be convinced of a party’s leadership, economic competence and sense of fair play.