If a week is a long time in politics, a century can seem surprisingly short. With uncanny timing, the centenary of the death of Keir Hardie, Labour’s first leader and arguably its most towering figure, falls at the end of this month, on the very weekend that Labour delegates will gather in Brighton for this year’s annual conference, the first under the party’s new leader.

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Hardie has long been claimed by all wings of the party. Possibly the most unlikely endorsement came from Peter Mandelson who suggested, back in 1992, that Hardie would have felt “rather pleased” with New Labour’s changes. In his failed bid for the Labour leadership in 2010, David Miliband made a far more cerebral case for Hardie as a self-help, rather than a statist, socialist. And earlier this summer, in this paper, Alan Johnson invoked the “pragmatism” of Labour’s first leader in support of the candidature of Yvette Cooper and New Labour’s record in office.

Likeable as Johnson is, his claim is politically disingenuous. Hardie was a far more radical figure than Johnson suggests, committed not to revolutionary political violence but to “agitation” and to stirring up “divine discontent with wrong” wherever he saw it. It was Hardie who finally pushed the TUC, for too long a stooge of the Liberal party, to support the eight-hour day. He backed the new unionism of the late 19th century, the aims and tactics of the suffragettes, and the (still) unpopular causes of republicanism and pacifism. Ridiculed and attacked by the press throughout his political life, he died an isolated figure a year into the first world war (which he bravely opposed) but is now remembered for his consistent stand against exploitation and injustice.

Facebook Twitter Pinterest ‘Keir Hardie disliked Westminster. He was not a good parliamentary leader and he knew it.’ Photograph: Hulton Archive/Getty Images

When it comes to the politics of agitation, Jeremy Corbyn is Hardie’s clear heir. Were Hardie alive in the 21st century he would surely have opposed the Iraq war, visited the Occupy encampments, supported those activists fighting against the “social cleansing” of London and denounced austerity. A charismatic public speaker who frequently addressed huge crowds, he would have recognised the enthusiasm and fervour of the mass audiences that Corbyn has attracted across the country, which so many thought dead in the age of Twitter and Facebook.

But Hardie also teaches us more subtle lessons about the past. His story reminds us that Labour has always been, if not quite two parties, a clearly uncomfortable mix of socialists and social democrats, those who instinctively distrust power structures and those who believe we need to engage with the institutions of the state in order to transform them. In 1895 Beatrice Webb, founder of Fabianism, records in her diary a stilted meeting between some early Fabians, Hardie and other leading union figures, which made painfully clear the split between those who wanted gradually to “inoculate” all classes of society to “collectivism”, as the Fabians called it, and a rawer, more instinctive drive to rectify injustice in the here and now. Sound familiar?

Too many commentators wrongly interpret the enthusiasm around Corbyn (I refuse to call it Corbynmania – support for his candidacy is not a psychiatric condition) as mere nostalgia for the certainties of the 80s. It has a much longer and shorter history than that. In it, we can hear the echo of the passionate principles of Labour’s founding leader and a many-layered rebellion against the style and content of the party’s direction in recent decades.

It is also part of a more positive impulse: to build up a new movement, working with idealists beyond the party’s borders. And it is not just among the young. I have lost count of the number of older, more politically middle-of-the-road members who have told me that Corbyn is the only candidate putting forward a raft of sensible solutions to what they now see as “broken Britain”, affecting middle and low income alike, with its high rates of unemployment, millions on low pay, an acute housing shortage and an unfeasibly expensive higher education system.

I refuse to call it Corbynmania: support for his candidacy is not a psychiatric condition

But Hardie’s political trajectory also serves as an important warning to any contemporary radical leader in parliament, the one bit of the job many claim Corbyn cannot do. A strong believer in representative democracy, Hardie nonetheless loathed the deal-making and elitism of parliament itself and was widely acknowledged as a poor leader of the party in the Commons for the very short period he undertook the job from 1906 to 1907. But then his near-contemporary, Ramsay MacDonald, Labour’s first prime minister, was a brilliant tactician who ultimately fell under the seductive spell of the rich and powerful and entered into a disastrous national government in 1931. When it comes to exercising power, it seems there are many ways to fail.

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There’s no doubt that a Corbyn win would pose an enormous challenge for the centre-right of the party, but the many MPs who oppose him can surely sit on their hands or plot, or both, for only so long. The task is even greater for the member for Islington North, borne in on a wave of popular feeling.

If his leadership were to succeed, it would need to be exceptionally generous, imaginative and inclusive. It would have to forge fresh alliances, take surprising positions and make unexpected compromises. Hardie the seer, the agitator, inspires those of us who believe Labour needs to present a bolder alternative to the Conservatives. Hardie the diffident party leader reminds us that we still have a lot to learn about how to shape “divine discontent” into a credible and popular programme.

• Melissa Benn will be in debate with Keir Starmer MP and Rafael Behr on “What Would Keir Hardie Say?” at the National Portrait Gallery on 3 September at 7.30pm