Henry Charles Keith Petty-Fitzmaurice, fifth Marquess of Lansdowne (1845–1927), personifies the positive qualities of the aristocracy. The reason these people were given fine educations, enormous privileges and almost unlimited leisure was so that they could offer disinterested counsel and dedicate their lives to the public good. If they had something important but unpopular to say, they would be so confident of themselves and their place in society that they would not care about the obloquy that would descend upon them. Lord Lansdowne was such a man. The hatred that erupted following the publication in 1917 of the so-called Lansdowne Letter, which called for Britain to negotiate a peace treaty with Germany, would have crushed a lesser man; for him it was merely the chirruping of the populace.

After Eton and Balliol, Lansdowne inherited, aged twenty-one, Bowood in Wiltshire, Lansdowne House near Berkeley Square (with its four-acre garden), 138,000 acres in Ireland, 10,000 acres in Scotland and an art collection that meant that when he got into debt he could sell a Rembrandt – one such work went for a record price of £100,000 in 1911. True to his Whig political inheritance, he became a Liberal Unionist and so was in government for much of his political life. This allowed him to undertake a life of public service that was extraordinary even by the standards of the Victorian and Edwardian higher aristocracy.

This extremely well-researched and well-written biography by Simon Kerry, who has a history doctorate from the University of East Anglia, shows that Lansdowne was much more than just a safe pair of hands. He was a statesman who would probably have become leader of the Conservative and Unionist Party instead of Andrew Bonar Law in 1911 had it not been for the peerages he inherited, which dated back to 1760. Although being a British peer was, of course, a huge advantage in many ways, for people like Lansdowne in 1911, Lord Curzon in 1922 and (thankfully) Lord Halifax in 1940, it effectively blocked them from the top job.

Lansdowne’s career represents the classic cursus honorum of British imperialism. He became a junior minister under Gladstone at twenty-seven, then undersecretary of state for India at thirty-five, clearly being groomed for the greatest post the Empire had to offer. He was governor-general of Canada from 1883 to 1888, during which time he put down the North- West Rebellion of 1885, for which some French Canadians still blame him. Having shown both diplomacy and a touch  of ruthlessness (he approved the hanging of the ringleader, Louis Riel), he proved that he could be trusted with Britain’s most senior proconsular post, viceroy of India.

Kerry is equally at home in the India Office archives as in the Bowood Collection. In all he has visited no fewer than thirty-nine different archives in his pursuit of original, previously unpublished information, which shows staggering dedication. Archival research has taken him to North Carolina, Paris, Ottawa, Vienna, Dublin, Washington, DC, Belfast and all over the United Kingdom mainland, suggesting that this book marks the arrival on the scene of a major new sleuthing historian of modern Britain. His efforts have been well rewarded by an avalanche of new material not mentioned in the only other biography of Lansdowne, which was published in 1929.

Lansdowne’s stint as viceroy of India from 1888 to 1894 was a success, but it has been somewhat overshadowed by that of one of his successors in the post, Lord Curzon. He nonetheless did achieve several notable successes, sometimes in the face of Hindu obscurantism, such as when he raised the legal age of consent from ten to twelve. In May 1890 Phool Mani, a child bride of eleven, died in the consummation of a marriage to a man twenty-four years older. Although some in the Congress party in India opposed it, Lansdowne demanded a change in the law to make marriage at such a young age illegal, despite accusations of unwarranted state interference in Indian family rights.

Lansdowne’s five years as secretary of state for war between 1895 and 1900 were dominated by the Boer War, and especially by the series of disasters that overtook the British in South Africa during Black Week in December 1899. He was not responsible for the bad generalship during that war but came under intense criticism as a result of it, including from such notable writers as Rudyard Kipling, Hector Munro (alias Saki) and J A Spender, the editor of the Westminster Gazette. Despite his lack of personal responsibility for such calamities as the Battle of Spion Kop – the unvarnished report  of which he bravely published, against official advice – Lansdowne offered to resign, not once but twice.

However, the prime minister, Lord Salisbury, recognised Lansdowne’s talent and did not blame him for the generals’ incompetence. Rather, he promoted Lansdowne to foreign secretary, an office he himself had held along with the premiership. Lansdowne served in this capacity from 1900 to 1905 and was thus instrumental in creating the Entente Cordiale with France, an alliance that was eventually, though at unconscionable human cost (including Lansdowne’s youngest son), to win the Great War.

It was at a critical moment in that conflict, on 29 November 1917, that Lansdowne published a letter in the Daily Telegraph – The Times having rejected it as not in the national interest – calling for a negotiated peace with Germany. ‘We are not going to lose this war,’ he wrote, ‘but its prolongation will spell ruin for the civilised world, and an infinite addition to the load of human suffering which already weighs upon it … We do not desire the annihilation of Germany as a Great Power.’

The effect was immediate; there was wholesale condemnation across the political and social spectrum. Lansdowne was abused as a traitor and H G Wells sneered that he only put the peace proposal forward because he feared a revolution that would strip him of his land and wealth, a wholly untrue allegation. Generals Haig and Robertson negated the force of the letter by speaking of an imminent victory, which actually took another year to achieve at the cost of hundreds of thousands more lives. Germany was left shattered, and within a decade was facing the rise of the Nazis Peace in the same month as the Bolshevik Revolution might even have given the West the opportunity to snuff out a creed that was to lead to the death of one hundred million people.

Of course, there were good arguments against Lansdowne’s proposal, and Kerry rehearses them in an admirably objective way. The most serious is that the Germans were in no mood to go back to the pre-war status quo, which was what Lansdowne wanted to offer, and would probably have rejected his proposal had it been made. Kerry’s explanation of the Lansdowne Letter is intelligent and convincing. ‘It spoke for his values,’ he writes, ‘values nurtured over a lifetime, values that he believed were worth salvaging from the pre-war world. That these values did not appeal or seem relevant to a younger generation added to the sensation it stirred up. He was quite unrepentant about it. Of course he was: he was an aristocrat.