An outcry greeted the memoirs — or at least the money paid for them. Was it right that a prime minister who had led his country in a bloody war should now make a huge profit for himself? After some awkward hesitation came an announcement that proceeds from the book would be "devoted to charities connected with the relief of suffering caused by the war. He feels unable to take any personal advantage for himself."

That was the summer of 1922 and the prime minister was David Lloyd George, still in office though not for much longer. This entertaining and illuminating biography was already off the presses before history repeated itself and we were told that the proceeds from A Journey would go to the Royal British Legion and so Roy Hattersley was unable to make any comparisons but they will strike his readers.

So much of what was written about Lloyd George, by himself and especially by Lord Beaverbrook, is unreliable, that a biographer has to begin by sifting through the mythmaking. The famous Welshman was born in 1863 in Manchester and his real name was "George" tout court but north Wales was where young David grew up and it would be his political base, even if he visited it as rarely as possible for most of his life.

Start of a political career

He later made much of his poverty-stricken childhood, far too much if other members of his family were to be believed. And if his formal education wasn't lengthy, it was sufficient for him to become a solicitor. He plunged into Liberal politics and in 1890, before he was 30, he had won a by-election for Caernarvon Boroughs, whose MP he would be for 55 years.

Like Disraeli, he was an exotic who knew he couldn't forge a political career by modesty and restraint. From the start, Lloyd George assailed his foes in savagely unfair language, with what Hattersley calls an entirely gratuitous attack on Joseph Chamberlain, and another rabble-rousing speech whose peroration was "absolute gibberish". A man who would lead his country to victory in one war became a national figure by denouncing another.

Lloyd George's speeches against the Boer War were broken up with great violence at one meeting — he had to escape through the back door disguised as a policeman and one Tory MP regretted that he hadn't been killed. Four years later Lloyd George was a cabinet minister and 15 years later he was prime minister heading a predominantly Tory government.

Some of the great questions of a century ago still resonate: the House of Lords; women's rights; the welfare state, whose foundations Lloyd George laid with his old-age pensions, paid for by (not very steep) taxes on the rich.

But a vast amount of time was spent on sectarian questions which are now as remote as the French Wars of Religion.

Lloyd George and his allies won their fight for the disestablishment of the Church in Wales. But protestant nonconformity is of no moment at all in modern England, or even Wales.

Who knows whether the "Campbellite Baptists", the little sect in which Lloyd George grew up, even still exists?

There are a few minor slips. Roger Casement was hanged rather than shot, not that it now makes much difference to him, and Irish history in general is not Hattersley's strong suit.

But when we come to the lurid drama at the end of 1916, Hattersley is excellent. He gives a clear account of the way Lloyd George supplanted Asquith as prime minister, challenging other versions. And so to the gruelling last two years of the war and Lloyd George's conflicts with the generals, the rupture in the Liberal party and the sordid four years of the coalition government he continued to lead after the war.

Sir Douglas Haig and the other "brass hats" had no idea how to win the war except by getting more and more of their men killed. But did Lloyd George have any more idea? He seems as bad an amateur strategist as Churchill. I was baffled by Hattersley's description of the plan Lloyd George hatched in 1915 to raise a large new British army, reinforced by "possibly 500,000 Romanians, Greeks and Montenegrins", to "land on the Dalmatian coast and attack Austria through Salonika", words which make no geographical sense at all.

Maybe the most striking thing about this book is Hattersley's distaste for Lloyd George, which becomes clearer with every chapter — and is an ironical reflection on its origins.

Shortcomings disclosed

Hattersley was urged to write it by Roy Jenkins, who himself disliked Lloyd George "so heartily that he could not contemplate writing the book himself". One feels that Hattersley wants to admire Lloyd George as a provincial radical and the proto-apostle of the welfare state. And yet the closer he studies his life, the more conscious he is of the man's faults.

He is notably harsher than the late John Grigg, a pious Anglican Tory, whose sympathetic, uncompleted multivolume life Hattersley makes good use of. So we learn about Lloyd George's lack of scruple and his use of any available ends to achieve his means.

Worse still were Lloyd George's hair-raising financial adventures, from fanciful gold mines to the Marconi affair to the blatant sale of honours. I was about to say primly that all this would have ended any political career today but then look! A.J.P. Taylor wrote that Lloyd George was the first prime minister since Walpole to leave Downing Street flagrantly richer than he entered it. But he was not the last.

Again and again, as I read this account of underhand political manoeuvres, of misrepresentation to the point of mendacity, of cash for peerages, of personal enrichment and then a guilty gesture of giving away some of the proceeds, I was reminded of a more recent occupant of Number 10. Might not the penultimate premier make the subject of Lord Hattersley's next unsparing biography?

David Lloyd George: The Great Outsider By Roy Hattersley, Little, Brown, 720 pages, £25