In our centenary issue of 12 April 2013, Tony Blair challenged the Labour Party to be “the seekers after answers, not the repository for people’s anger”. “In the first case, we have to be dispassionate even when the issues arouse great passion,” he wrote. “In the ­second case, we are simple fellow-travellers in sympathy; we are not leaders. And in these times, above all, people want leadership.”

Mr Blair has become an embarrassment to Labour, not least because of his misadventure in Iraq and his less-than-distinguished activities in retirement. Yet his insight that Labour could not prevail if it appeared to be merely an instrument for expressing discontent with the Conservatives, rather than a means to a bold transformation of British society, was proved painfully correct on 7 May. And this much is true: since Harold Wilson resigned as prime minister in 1976, Labour has had seven leaders but only Mr Blair has proved ­capable of winning a general election.

In a passionate essay also published in this week’s issue, the actor and activist Michael Sheen echoes Mr Blair when he writes, “The question of whether Labour moves back towards the centre, doing more to seem business-friendly or breaking away from the unions, is totally secondary to the fundamental question: ‘What do you believe in?’” To which he adds a second question: “How do you turn that into policy that can make concrete change?”

Despite his heavy defeat, Ed Miliband did a good job of answering the first question. He was rightly offended by deepening inequality and, in an age of globalisation, by the widening gap between the very rich and the rest – the pressing issue of our time. Whichever politician emerges to lead Labour should not abandon the fundamental insight that deep inequality corrodes the soul of a nation.

Mr Miliband failed, however, to provide an answer to the second question posed by Mr Sheen. Under his leadership, Labour’s policy solutions were quotidian and incremental. Rather than setting the mood of modern Britain, Labour fell victim to it. For the left, in particular, this is an era of easy anger. Political action all too often begins and ends with shouting at a computer screen. That old phrase – “The right seeks converts, the left seeks heretics” – is truer than it has ever been. Mr Miliband attempted to channel people’s anger, even going so far as to persuade Russell Brand to endorse Labour. But the idealism of the young proved an inadequate weapon against the caution of the old. Labour led the Conservatives by 16 points among first-time voters but trailed by 24 among the over-65s, who also voted in far greater numbers.

Labour will not return to power if it seeks to win only the votes of those who are angry at the condition of modern Britain. It must also win the support of those who are doing well – and, indeed, the support of those who live so precariously that talk of change feels like a threat, rather than a blessing.

On all but the rarest of occasions, no single party can achieve all it wants. Even movements of the left and centre left require compromise, with one another as well as with the country at large. This can only be achieved through collective endeavour and complex trade-offs. Understanding the cause of left-wing anger – but being more than a mere repository for it – will be the biggest task of whoever emerges as Ed Miliband’s successor from a protracted leadership campaign.