Winston Churchill once quipped that Clement Attlee, who was deputy prime minister in the wartime coalition and led the Labour party for 20 years from 1935, was “a modest man with much to be modest about”. For Aneurin Bevan, who in 1951 resigned from the Labour cabinet over the imposition of charges for dentistry and spectacles, Attlee’s radicalism was compromised by his “bourgeois values”. For George Orwell, he was a “dead fish”. In a 1955 profile, the New ­Statesman praised Attlee’s integrity while damning him for a lack of imagination. Why, the magazine asked, “should so conventional and Conservative-minded a man allow himself to become the leader of the British Labour party”?

This, in essence, is the question that John Bew attempts to answer in his long and fascinating biography of Labour’s greatest prime minister. Bew is an academic historian, biographer, journalist and foreign policy specialist. He writes with flair and considerable intellectual confidence, and is particularly good on Attlee’s essential petit bourgeois conservatism (which so irritated Bevan), in upbringing, disposition and motivation.

Born in 1883, Attlee was the son of a prosperous City of London solicitor, and was educated at Haileybury College, in Hertfordshire, and at Oxford. With close historical ties to the East India Company, Haileybury had a strong military and imperial ethos, and this appealed to Attlee, whose favourite poet was Rudyard Kipling.

After Oxford, he qualified as a barrister and began working as a volunteer in the East End at his old school’s Haileybury House mission in Stepney and at Toynbee Hall. It was said that Attlee “matured into socialism”, and his experiences in the East End certainly awakened him to the struggles of the poor. At the age of 31, he enlisted to serve in the first world war, and was wounded at the Battle of Hanna in Mesopotamia.

These early years are extensively covered in this new biography because they shaped what the author calls Attlee’s “unobtrusive progressive patriotism” — something that Bew feels has been lost from the Labour party today. Attlee was not a jingoist or imperial adventurer — unlike Churchill, he supported Indian independence — but, as Bew puts it, he believed that “love of country could be a noble and unifying theme”.

Any reconsideration of Attlee, who is claimed by both wings of the party, is particularly relevant now as Labour descends deeper into civil war. Under the leadership of Jeremy Corbyn, the party has been captured by the far left and its MPs have allowed themselves to be disempowered because of the foolishness of their decision-making. Meanwhile, the Corbynites are successfully transforming Labour into a mass-membership movement of anti-capitalist activists, many of them radicals drawn in from fringe groups as well as other parties, such as the Greens and Respect.

Labour has long had a strange relationship with its leaders. Consider the Christian pacifist George Lansbury, who was toppled in 1935 because he opposed rearmament and is remembered today, if at all, as a well-meaning fool; or the hapless Ed Miliband, who not only lost Scotland but introduced the revised rules by which the party elects its leader and thus opened the way for the Corbyn insurgency. Then there is Corbyn, despised by his MPs but adored by the activists — at least for now. Or consider how the party has come to loathe Tony Blair (one reason for Corbyn’s popularity) just as it has long loathed Ramsay MacDonald, who abandoned Labour to lead the National Government.

There is a sense, too, that in government — especially in government — the Labour party betrays its historical purpose by too easily making peace with capitalism rather than fundamentally reforming or seeking to overturn it. Throughout much of his leadership, Attlee was hounded by the left, who disliked his caution and believed that he did not understand economics. It was no easier for Harold Wilson, who came from the left of the party (he resigned from the cabinet alongside Bevan in 1951) but ended up operating mostly as a pragmatic centrist, as later did Neil Kinnock in different but equally fraught circumstances. He was a former soft left, anti-nuclear campaigner who lost two general elections but helped make the party electable again by dragging it towards the centre after the Bennite wars of the late 1970s and early 1980s.

Gordon Brown, who was as much the creator of New Labour as Blair, was deeply learned in Labour history and had a sense of moral mission. But as chancellor, for all his sermonising, he accepted the neoliberal settlement, and admired the Adam Smith of The Wealth of Nations just as much as he did the Smith of The Theory of Moral Sentiments.

By the time Brown entered 10 Downing Street, it was already too late for him: the Iraq war and the financial crisis had destroyed the credibility of New Labour. Having complacently believed that he could bend the forces of capitalism to his will, prime minister Brown was punished for his paranoid style and the Faustian bargain he had made as chancellor with the City of London.

All of this explains why many Labour people are increasingly nostalgic for the Attlee government of 1945-51, and some even demand a return to signature policies of the era such as nationalisation of the railways. But as Bew reminds us, the road to the postwar Labour transform­ation of society was smoothed by very particular historical circumstances — the wartime command economy, the Marshall Plan, the Beveridge Report and Keynesian economics, working-class solidarity, austerity and rationing, the widespread belief sweeping Europe that socialism was the future.

Many of the Attlee government’s achievements — the National Health Service, the welfare state, the com­m­issioning of Britain’s independent nuclear deterrent — were lasting. Even today, no Conservative government dares to dismantle the NHS or roll back the state in the way that former chancellor George Osborne, in his more utopian moments, yearned to do.

Yet the left often forgets or ignores just how beset by problems the Attlee administration was, from the 1949 devaluation of the pound to the resignation of Bevan and the emergence of the leftwing Bevanite faction. Within six years of Labour winning a 146-seat majority in 1945, Winston Churchill was prime minister again, the beginning of another period of Tory rule.

“Much of what Attlee achieved was tied to a twentieth-century project,” Bew writes. “If something is salvageable from his government’s legislation, it is ethos rather than process.” This insight seems right to me. Bew believes that Labour has lost a sense of historical mission and too easily forgets that having rights also entails having duties, obligations and responsibilities.

Attlee may have been a Victorian moralist but he was never priggish or sanctimonious. He knew he was fortunate, but living and working among the East End poor altered the course of his life. Above all, he never stopped loving Britain, in the service of which he was prepared to die and which in his autobiography he called the “greatest country in the world”.