Sir Bernard Crick belonged to an endangered species. He was a public intellectual in the mould of the great socialist sages of the first half of the last century — Graham Wallas, G. D. H. Cole, R. H. Tawney and Harold Laski. He was a distinguished political theorist, with three important scholarly works to his credit, as well as one great one.

He also intervened incessantly in public debate, on matters ranging from parliamentary reform to the politics of divided societies. But his academic works and his essays and journalism dealt with the same themes, and were written in the same accessible, slightly quirky and occasionally waspish style.

Not for him the gnarled prose of the self-consciously professional scholar, or the windy exaggerations of the media columnist. He wrote for another endangered species — the educated and thoughtful general reader.

His best-known book is probably his George Orwell: A Life, a biography commissioned by Orwell’s second wife, Sonia, and published in 1980. The biography won Crick great public réclame but led to a breach with Sonia, who thought it had not done justice to the subject.

In truth, Crick was too much the political theorist, and perhaps too lacking in human empathy, to be a natural biographer. His treatment of Orwell the novelist, polemicist and (not least) prose stylist was scrupulously thorough, but Orwell the man never quite came to life.

Of much greater long-term significance than Crick’s Orwell was his glittering masterpiece, In Defence of Politics, first published in 1962, when he was only 33. It was a young man’s book, written with exhilarating panache. It was translated into four languages, and went through five editions.

It set out an essentially republican vision of politics — of politics as freedom and of freedom as politics — heavily influenced by the great German Jewish political philosopher, Hannah Arendt, and ultimately derived from Aristotle.

Thanks partly to Crick, that vision is now quite common; indeed a whole academic industry is now devoted to the republican themes that Crick brought back into public consciousness. But in 1962 he swam against the current. Parliamentary politics were dominated by the twin paternalisms of Fabian centralism on the left and noblesse oblige Conservatism on the right. In the academy, political scientists had retreated from civic engagement into pseudo-scientific number-crunching or a weary quietism.

Against these orthodoxies Crick raised a flag of revolt. He sought to return to a much older tradition of political thinking, centred on active and participatory citizenship in a pluralistic political community.

Politics, he insisted, was not universal. It had been absent from many, perhaps most, societies known to history. It was not an ideology: ideology was one of its most dangerous enemies. It was not to be equated with democracy. Unrestrained democracy — democracy as a euphemism for mob rule or as camouflage for the tyranny of the majority — was another enemy. Politics was about conciliation, compromise, argument and debate between diverse groups. It was grubby and unheroic; negotiation and deal-making were of its essence. Yet only by and through it could free men and women live together in society. But there was nothing inevitable about it. It depended on “deliberate and continuous individual activity”.

“Activity” was the key word. Crick was not content to theorise. He wanted to do what he could to realise his vision of politics in the real world of practice. In that spirit he published The Reform of Parliament in 1964, and helped to set up the Study of Parliament Group in the same year.

The Reform of Parliament had none of the sweep and élan of In Defence of Politics. In effect, it was a rather decorous manifesto, setting out the case for more effective parliamentary scrutiny of the executive, while preserving the essentials of the British parliamentary monarchy.