David Lloyd George was self-created and self-destroyed. His self-destruction, after 13 remarkable years in which he almost single-handedly launched the welfare state and mustered the drive to defeat Germany, can be dated to one fateful act in November 1918. The decision to forge a peacetime coalition with the Conservatives undermined his reforming credentials and eviscerated the Liberal Party. Within six years, the Liberals shrank from 258 to 40 seats in the House of Commons, replaced by Labour as the principal vehicle for progressive politics.
Andrew Bonar Law, the Conservative leader, boasted in a 1918 election message to Tory MPs cited by Roy Hattersley: "It is not his Liberal friends, it is the Unionist Party which has made him prime minister." He added, for the Tories rarely take their eye off the ball of power: "Remember that at this moment Mr Lloyd George commands as great an amount of influence in every constituency as has ever been exercised by a prime minister in political history."
Less than four years later, Lloyd George having tried but failed to form a "national" party uniting Tories and coalition Liberals, his popularity waning amid recession, spending cuts and traumatic events in Ireland and Europe, Bonar Law engineered his downfall and seized the keys to No 10. The Welsh Wizard never held office again. Not that he lacked radical themes thereafter, or failed to inspire barnstorming campaigns. The Yellow Book of 1928, much of it the work of John Maynard Keynes, was the best interwar blueprint for tackling unemployment and modernising industry.
Had Ramsay MacDonald and Philip Snowden sided with Lloyd George and Keynes, rather than Stanley Baldwin and the Bank of England, the economic laissez-faire of the 1930s might have been averted by a British version of FDR's New Deal advancing under a progressive Lab-Lib coalition. As Hattersley remarks: "LG had become a thoroughgoing Keynesian and, as such, in economic policy, both ahead of his time and a social democrat." But the Liberals were too weak to enforce Lib-Labbery, and Labour's distrust of LG was too visceral. Keeping LG out of office was the strongest bond uniting MacDonald and Baldwin in the National Government of 1931. When Baldwin was succeeded by Neville Chamberlain, who had an equal determination to keep out Winston Churchill, Lloyd George's comrade-in-arms for most of his 17 years as a minister, the catastrophe of the 1930s was complete - all of it with roots deep in the Con-Lib coalition of 1918-22.
Hattersley declares in his opening words that Roy Jenkins suggested the idea of this biography of Lloyd George, "a politician he disliked so heartily that he could not contemplate writing the book himself". It would help uninitiated readers if he explained why. Jenkins was not only Herbert Asquith's biographer, but Asquithian to the core, modelling himself on the Balliol-trained, urbane, broad-minded Liberal leader. Asquith's enemies were Jenkins's enemies, Lloyd George foremost among them after their wartime split in 1916. For all its empathetic brilliance, Jenkins's 1964 biography fails to acknowledge Asquith's manifest unfitness as a war leader. It also skates over his womanising and excessive drinking.
By contrast, Hattersley's judgements on Lloyd George are good and dispassionate throughout, and the veil is not so much lifted as ripped from his private life. After 1913, he had two wives: Margaret in Criccieth, Caernarfonshire, with the children, and Frances Stevenson, his constant secretary-mistress in London and at his new country house at Churt in Surrey. Frances's daughter Jennifer was probably by Lloyd George, or possibly from a parallel affair between Frances and one of Lloyd George's staffers. These tales are fully told.
None of this gainsays Lloyd George's triumphs as "the authentic radical of British history". Without his bold liberalism, there would have been no progressive People's Budget of 1909, no "peers v people" elections in 1910, no abolition of the veto for the House of Lords in 1911, and probably no health and unemployment insurance before the First World War.
Nor would there have been the spell-binding popular oratory, admired by Hitler and Lenin alike and unmatched by any British politician of the 20th century apart from his fellow Welshman Aneurin Bevan. Lambasting the Boer war, fighting the Germans, excoriating the Lords and the established Church, exposing injustice - his every cause was a demotic crusade, fought ad hominem, and arousing not just excitement, but hysteria.
Lloyd George's achievements were vast. However, it is important to understand that they resulted not only from his liberalism and his oratory, but also from his huge capacity to forge partnerships and energise the process of government. Until the collapse of his coalition, he got big things done. With Asquith, he launched the welfare state and emasculated the peerage. With Bonar Law, Arthur Balfour and Douglas Haig, he won the war. With President Wilson, he negotiated a peace settlement.
This necessarily qualifies Hattersley's subtitle: The Great Outsider. Lloyd George became a versatile insider, a government man adept at compromise, constantly hankering for coalitions and combinations to co-opt the very Conservatives and monopolists he condemned on the platform. He used them, but they used him just as much.
Lloyd George's taste for coalition-building long pre-dated 1918. Throughout the fluid politics of 1910, with its two kings, two elections and constitutional crisis, he was flattering Balfour in private with coalition schemes. It was essential, he argued, to unite "the resources of the two parties into joint stock" in order to avoid "imminent impoverishment if not insolvency". He also toyed with a government "composed of businessmen which would carry enormous weight in the country".
This is the paradox of Lloyd George, outsider and insider, siren and sycophant. The paradox, perhaps, of British liberalism, as exemplified by William Gladstone and Charles Grey, the greatest 19th-century Liberal leaders, though they both avoided Tory coalitions and preserved their party. Hattersley paints a splendid portrait of this genius of modern liberalism. Keynes evoked him best: "How can I convey any just impression of this extraordinary figure of our time, this siren, this goat-footed bard, this half-human visitor to our age from the hag-ridden, enchanted woods of antiquity?"
David Lloyd George: the Great Outsider
Little, Brown, 720pp, £25
Andrew Adonis is director of the Institute for Government. He was transport secretary in the last Labour government.