During his bid for the party leadership in 2010, Ed Miliband named Clement Attlee as the politician he most admired – something he repeated in an interview in June this year. His definition of Labour’s “one nation” mantra also contains a nod to the “spirit” of the transformative Attlee government elected in 1945. Yet the “one nation” theme is, of course, taken from the Conservative Party. And it was not to any Labour greats that Miliband turned in his 10 September speech to the TUC conference, but to two 19th-century Conservative prime ministers. The first was the Earl of Derby, who legalised trade unions in 1867. The second was Benjamin Disraeli.

According to Miliband, David Cameron has governed in the interests of a privileged few and thereby failed to meet the standards set by his Disraelian forebears. Whether or not this message is starting to get through to the electorate, it is an unusual standard for a Labour leader to set. In truth, the act of scavenging in Tory history shows something else – which is that the Labour Party has a tortured relationship with its own past, particularly with those who have delivered its greatest successes.

The disavowal of Blairism is inevitable, perhaps, for the time being at least. But the failure to understand Attlee – the man himself, rather than simply the government he led – points to a larger failure of political imagination. Attlee remains, in the memorable phrase of Vernon Bogdanor, Cameron’s old tutor at Oxford, “the enigma of 20th century British history”. Surprisingly, however, it is those on the left who seem to have most difficulty in understanding him, or in coming to terms with the (sometimes uncomfortable) political lessons that he bequeathed his party.

The irony of this is that no figure in modern British political history encapsulates the true “one nation” spirit better than the man who led Labour to its landslide victory in 1945 and secured its highest ever share of the popular vote in 1951. Attlee would “get it”, even though his party has often struggled to get him.

The family tie between Labour and Attlee has long since snapped. In 1997, his grandson John, who inherited his title as the 3rd Earl Attlee, crossed the floor of the House of Lords to join the Conservative Party. He said that his grandfather would be “horrified” by the party Labour had become. John’s father, Martin, the 2nd Earl, left Labour in 1982 and became a founding member of the Social Democratic Party.

It was Ralph Miliband, taking his cue from Harold Laski, who did most to denigrate Attlee’s approach, with his 1961 book Parliamentary Socialism. Both Miliband sons have distanced themselves from their father’s criticism of a Labour Party “of modest social reform in a capitalist system within whose confines it is ever more firmly and by now irrevocably rooted”. Yet Ed Miliband’s evocation of Attlee says more about the circumstances in which he found himself leader than it does about Attlee. First, it is a means of distinguishing himself from Blair. Second, at a time of economic downturn, Attlee’s postwar government is being held up as a model for what bold reforms might achieve, regardless of austerity. “Despite a huge deficit we built a national health service,” Miliband has said of that period. What Attlee the man stood for, and the principles on which his government was founded, remained unexplored.

As the Observer put it in a profile of Attlee in June 1944, he was a “co-ordinator more than creator”. He was often overshadowed by the “big beasts” around him – Ernest Bevin, Aneurin Bevan, Herbert Morrison, Stafford Cripps or Harold Laski. “A little mouse shall lead them,” remarked another of these heavyweights, Hugh Dalton, when Attlee became party leader in 1935. Or a “little nonentity”, as Beatrice Webb put it in 1940.

Attlee’s parliamentary career, which began in 1922, was a lesson in consistency, coherence and staying power. “Men who lobby their way forward into leadership are the most likely to be lobbied back out of it,” he once quipped.

“How could so modest, almost diffident, laconic a man ride all these political storms and remain serenely afloat?” asked Douglas Jay, the Labour MP. The best recent biography of Attlee, by Nicklaus Thomas-Symonds, argues that his modest leadership style was an advantage (in securing the loyalty of Bevin, for instance) and occasionally a curse (mishandling Bevan before his resignation in 1951). There was luck – he was one of the few Labour MPs to survive the electoral wipeout of October 1931 – and there was political skill, as might be expected of the longest-serving leader of any mainstream British party in the 20th century.

This is not the stuff of legend and may not be particularly helpful today. Attlee was deeply resistant to media training and spin, confessing that he had “none of the qualities which create publicity”. That said, his description of the qualities required of a prime minister have a certain resonance. “Ah! A sense of urgency, of despatch. A sense of the time and the occasion and the atmosphere of the country,” he once said. Political judgement was “not the same thing as intellectual power, often quite divorced from it. A lot of clever people have got everything except judgement.”

Are there practical lessons to learn from the experience of the Attlee government from 1945 to 1951, as Miliband suggests? The context in which Attlee operated was so different as to make any technocratic analogies far-fetched. Nationalisation took place in an altered economic environment, brought about by the imperatives of wartime planning. The foundation stone of welfare reform was the revolutionary assumption – which represented the definitive break from 1930s Treasury orthodoxy – that full employment was possible and economically viable.

If economic recovery is today’s political priority, it is also worth remembering that the wheels of the postwar revival began to fall off from 1948. It has even been argued that the government might have created better long-term conditions for socialism by postponing welfare reforms and focusing instead on the type of national reconstruction programmes undertaken by French planners and German social marketers. As the Anglo- German sociologist Ralf Dahrendorf once put it: “All that they did was wonderful but clearly wrong – right in social terms, wrong in economic terms . . . It was the right government at the wrong time.”

On the modern left, two versions of the Attlee government from 1945 to 1951 predominate. One is a eulogy to the revolutionary legislative achievements of the period, such as the creation of the National Health Service and the William Beveridge-inspired welfare reforms, as witnessed in Danny Boyle’s London Olympics opening ceremony last year. The other, hinted at in Ken Loach’s film The Spirit of ’45, is a story of how the “New Jerusalem” of a socialist consensus was betrayed in the postwar years by proto-Blairites on the left.

Just as Boyle’s version is sentimental and unspecific, so Loach’s is sectional in a way that Labour’s victory never was. The enduring appeal of the Beveridge report was not that it represented a victory for the working class, or socialism per se, but that it provided a benchmark of social reform around which the nation could coalesce. It was the universality of provision which was intended to form the basis of a new contract between citizen and state. It is worth remembering that it was a system which was supposed to be measured by its social outcomes, rather than the amount put into it by the government.

In that sense, it is worth reconsidering the ethical basis of the Attlee government’s reforms on pensions, health and welfare, even if they were developed against a completely different industrial and demographic framework from what we have today. It is notable, however, that those who have already done so – such as Frank Field MP – have come up with conclusions that many in the party are not entirely comfortable about.

In 2005, when Field was asked to consider what Attlee would make of the modern welfare state 60 years after Labour’s victory, his response was telling: “Attlee would be likely to be devastated on the change in attitudes to welfare. He believed that welfare was important because each individual had an inherent worth which a minimum welfare provision reflected. But the idea that one would claim welfare as a right without first accepting one’s duties would be abhorrent to him.” In many ways, the social dimension of Blairism represented a return to the New Liberalism of T H Green. That Attlee consciously broke with the New Liberal tradition in 1945 – and moved towards a much more statist, redistributionist model – meant that he was not an easy figure for New Labour to appropriate. That those loosely associated with the Blue Labour wing of the party are more comfortable on this terrain is unsurprising.

In October 2011, Jon Cruddas, the Blue Labour thinker who is leading the party’s policy review, delivered the annual Clement Attlee Memorial Lecture at University College, Oxford. He had never been particularly sympathetic to Attlee before then, preferring the socialism of “human virtue, creativity and self-realisation” of his hero, George Lansbury.

Yet, challenged to explore Attlee further, Cruddas discovered that “there remains a sense of something hidden deep within the character of the man”, which even his best biographers had missed. Cruddas correctly pointed out that “the essential elements” of Attlee’s character were in place before 1914. In other words, the essence of Attlee is contained not in the “spirit” of 1945, but in all the life that came before it, including the two world wars. He fought in the first with distinction, and in the second he served by Winston Churchill’s side in the war cabinet.

In many ways, Attlee is the pivot on which 20th-century British history turns. To fail to understand his political life is to miss some of the most important lessons – and unspoken truths – of British political life.

More than any other British prime minister of the past century, Attlee provides a clue to the things our modern political classes are most uncomfortable or awkward talking about: ethics, Britishness, loyalty, patriotism, duties and rights.

Born and bred in middle-class south-west London, he found his ideological home in the working-class East End. He greatly enjoyed the poetry of Rudyard Kipling, but adapted Kipling’s imperialistic verse to the conditions of the English working class and, when prime minister, brought an end to Britain’s empire in India. Indira Gandhi once said that he embodied the “non-imperial face” of Britain, “a reassuring counterweight to the haughty mien of the Raj in India. I came to appreciate the understatement which characterises the best in Britain and of which Lord Attlee was a good example.”

One reason for his stunted legacy is that he never styled himself as a deep thinker in the way that many of his peers did. Despite his familiarity with socialist ideals, he was cautious about uncritically imbibing the prescriptions of leftist theoreticians. His estimation of G D H Cole was typical: a “brilliant chap” with “a very clear mind”, but “he used to have a new idea every year, irrespective of whether the ordinary man was interested in it or not”.

Attlee’s core values were neither mysterious nor exotic; they were strongly held, simply presumed, and widely shared across Britain. For that reason, they did not need elaborate definition.

The driving conviction of his life was a belief in public service. In October 1905, he volunteered at a boys’ club in Stepney, east London, more out of a sense of duty to his old school, Haileybury in Hertfordshire, which supported the club, than for any ideological reasons. The experience of the East End confirmed to him just how destabilising was the scourge of casual labour and the unfair operation of the old Poor Law of 1834. Visiting Essex Hall, he encountered the work of the Fabians for the first time.

Guided by his elder brother Tom, a Christian socialist, he began to read the work of John Ruskin and, as Attlee described in typically matter-of-fact fashion, “came to the conclusion that the economic and ethical basis of society was wrong”.

Attlee’s unwillingness to theorise should not disguise the richness of his political thinking, or the authenticity of his place within the British socialist tradition. He had prints of Marx and Engels on the wall of his office and once raised the red flag over Limehouse Town Hall. But what appealed to him about the Independent Labour Party, over the Fabians, was that it was never “rigidly dogmatic”.

“It was inclusive rather than exclusive,” he later explained, “and it preached a socialism which owed far more to the Bible than Karl Marx . . . a characteristically British interpretation of socialism, a way of life rather than an economic dogma.”

Toynbee Hall, of which he became secretary, had been started by Canon Barnett and his wife as a Christian mission that sought to eradicate poverty by encouraging a moral revolution among the working classes. As for his personal faith, Attlee once remarked: “Believe in the ethics of Christianity. Can’t believe in the mumbo-jumbo.”

As Frank Field has suggested, Attlee’s background made him “attach absolute meanings to such concepts as duty, responsibility, loyalty and courage”. By the same token, class conflict was anathema to him. Commissioned by the government to explain the workings of Lloyd George’s National Insurance Act 1911, Attlee recounted how he “admired the public spirit of the country notables”, mostly Tories, who had been bitterly opposed to the act but who co-operated with its implementation after it became law – both “one nation” and “big society” in their truest sense.

According to Lord Longford, Attlee was “not only the least selfish politician of the first rank . . . but the most ethical prime minister in the whole of British history”. He lacked the “Christian earnestness of Mr Gladstone”, but was “happily without the latter’s power of self-deception”.

And it is worth noting that this ethical purview extended to foreign affairs. He was a committed anti-fascist and anti-communist. He supported intervention on behalf of the patriot cause against the fascists in the Spanish civil war, coming up against the realism of others in his party such as Bevin.

For much of the 1930s he believed that the League of Nations was the best guarantor of collective security, but as its authority collapsed, he became a critic of the appeasement of Nazi Germany and of Neville Chamberlain’s disastrous efforts to treat with Hitler at Munich. It was Attlee who steered Labour away from both pacifism and passivism in foreign affairs, thereby passing the first test of an aspiring party of government.

His proudest act was to join Churchill’s wartime coalition in 1940. His favourite cartoon was David Low’s “All behind you, Winston” of May that year, which depicted the Labour triumvirate of Attlee, Ernest Bevin and Herbert Morrison rolling up their sleeves and marching into war alongside Churchill. Many years later, his wife contacted Low to buy the original.

The formation of the coalition government in 1940 is perhaps the most important moment in modern British political history. It ensured the type of national cohesion and feeling of common purpose that was absent at the outset of the war, and without which the fight could not have been sustained.

Monitoring early wartime broadcasts at cinemas across the country, British intelligence officers reported that Attlee’s flat cap was “said to have had a depressing effect on picture-goers”. Yet, though his presence was not inspirational, he – more than anyone – was the glue that kept the coalition together. Morrison was prevented from destabilising it, and Bevin was fastened to his side. As deputy prime minister, he managed to combine faultless loyalty to Churchill with primary responsibility for domestic affairs, preparing the ground for the revolution that was about to take place in the role of the British state. In his mind, the two causes – victory and reconstruction –were inseparable.

When he became prime minister on 26 July 1945 Attlee was shocked. Yet, as one of his MPs remarked, his victory speech was “typical”, in that it was delivered “without a trace of emotion”. Hype and triumphalism were not in his make-up and that fact, to some extent, had been crucial to the victory. The party the electorate had chosen was the dutiful, patriotic and measured entity that Attlee embodied from 1940 to 1945. Indeed, even as Laski attempted a coup against him before the election – a “what if” moment for the Ralph Miliband generation – it was Attlee who provided the reassurance that Labour’s New Jerusalem was nothing to be feared.

“The old school tie can still be seen on the government benches,” he assured the American government. Indeed, he was likened to Harry Truman, the US president with whom he built a sound working relationship. Addressing both houses of Congress in Washington, DC in November 1945, he was clear that his party’s political creed stood within the Anglo-American tradition of freedom but remained uniquely British in its version of socialism.

“You will see us embarking on projects of nationalisation,” he told the legislators, “on wide all-embracing schemes of social insurance designed to give security to the common man. We shall be working out a planned economy. You, it may be, will continue in your more individualistic methods.”

After 1945, his record in dealing with the Soviet threat was strikingly assertive and bold, and – together with his foreign secretary, Bevin – he played a leading role in the formation of Nato. Like Bevin, he was convinced that the atomic bomb was crucial to the projection of British power in the world. Rather than have a showdown with Labour ministers who opposed the bomb, such as Stafford Cripps and Hugh Dalton, he formed a secret committee to push the plan through before objections could be raised. Above all, he was a ruthless but consistent proponent of a strong tradition of left-wing British patriotism, at home and abroad. If “Attleeism” is anything, it is this.

Harold Wilson’s wife, Mary, once recalled having a conversation with Attlee towards the end of his life, in which she told him that her favourite characters in history were the “romantic ones”: Charles II, Rupert of the Rhine and Byron. His response was telling: “Bad history, wrong people.”

In attempting to reconnect with an increasingly sceptical public, the Labour Party of today could do worse than rediscover its own unromantic hero. The left may have struggled to understand him; but the nation did.

John Bew, a New Statesman contributing writer, is reader in history and foreign policy in the war studies department at King’s College London. From October, he will take up the Henry A Kissinger Chair in Foreign Policy and International Relations at the Library of Congress in Washington, DC.