Few people have heard of R B Haldane today. If he is known at all, it is as an obese Edwardian politician who was sacked from the Cabinet for being pro-German in the First World War. John Campbell is faced with the problem of making a case for remembering him. He argues persuasively that Haldane stood for a type of statesmanship that should give ‘a message of hope for all who despair in our present political climate’.

The first part of the book takes ‘deep dives’ into the personal foundations of that statesmanship. Campbell’s account of Haldane’s family background is masterly. Haldane came from an old aristocratic Scottish family with a strong tradition of public service, especially in the law. Educated in Edinburgh, he was sent to the University of Göttingen aged seventeen, and this was the start of a lifelong immersion in German idealist philosophy. But he didn’t pursue a career as an academic. He went to London and instead became a barrister. A QC at thirty-three, he earned a fortune.

One thing that emerges strongly here is Haldane’s dedication – one might say addiction – to work. He worked eleven- or twelve-hour days throughout his life, and thought nothing of reading until four in the morning. He played no sports but he loved dogs and he enjoyed plodding around his estate at Cloan with a St Bernard named Kaiser. Apart from work, his chief interest was eating. As Beatrice Webb wrote, he divided his time between ‘highly-skilled legal work’ and ‘digestion’. Everything was of the best – his cigars, his wine and his cook.

Haldane never married. He wrote every day to his mother, a tough old bird who lived to a hundred (these letters form the chief source for this book). He was twice engaged and each time the woman broke it off. The recently discovered letters that he wrote over a period of thirty years to Frances Horner, the chatelaine of Mells Manor and muse of Edward Burne-Jones, reveal a new and unexpected side to the philosopher-politician. This was a romantic relationship typical of the kind found in the intellectual political clique known as the Souls, and there are strong similarities with Arthur Balfour’s lifelong friendship with Mary Elcho. There was little or no sex and lashings of Goethe. Haldane left Frances £5,000 (worth roughly £300,000 today) in his will.

Aged twenty-nine, he became Liberal MP for Haddingtonshire. He visited Oscar Wilde in prison and provided him with the pen, ink and books that enabled him to write The Ballad of Reading Gaol. He was a friend of Natty Rothschild and acted as legal adviser to N M Rothschild & Sons bank. Together with his fellow barrister Herbert Asquith and Edward Grey, he formed the political group known as the Liberal Imperialists. These centrists were the Blairites of their day and they emerged as the dominant force within the Liberal government of 1905.

Haldane’s political career culminated in his appointment as Lord Chancellor in 1912, upon which he wrote to his mother, ‘I feel that it is the place you have always desired for me.’ But his success was short-lived. The outbreak of the First World War saw Haldane become the subject of a vicious smear campaign orchestrated by the Northcliffe press. He was accused of being a German spy and an enemy of the state. It’s true that Haldane was a Germanophile and regretted the outbreak of the war; in 1912 he had led the so-called Haldane Mission to negotiate a reconciliation between Britain and Germany. However, he did nothing to betray British interests and today Haldane seems courageous and far-sighted in speaking out.

The low point came in 1915. When the wartime coalition government was formed, the Conservatives insisted on the exclusion of Haldane from the new Cabinet. The prime minister, Asquith, who was supposedly Haldane’s oldest friend, made no real fight to keep him. Haldane didn’t attempt to vindicate himself, but he was wounded by Asquith’s betrayal and even more hurt by Asquith’s subsequent failure to clear his name publicly, which inflicted lasting reputational damage.

The sacking of Haldane was particularly unfair because he, more than any politician, had ensured Britain’s preparedness for war in 1914. As secretary of state for war between 1905 and 1912, he had been responsible for the creation of the British Expeditionary Force (BEF), a reform requiring extraordinary organisational powers. The BEF played a crucial role in coming to France’s aid to block the German advance towards Paris in 1914.

Haldane’s exclusion from the coalition was not the end of his career. He re-emerged as a minister in the first Labour government, when Ramsay MacDonald appointed him Lord Chancellor and leader of the Labour Party in the House of Lords. The man accused of treachery was once again one of the highest officers of state.

The author must be congratulated on shaking up the creaking cradle-to-grave style of conventional political biography. The book begins with an engaging account of the twelve-year-old Campbell going to stay at Cloan, then the home of Haldane’s nephew, inappropriately dressed in a new, shiny suit. Campbell has been an admirer of Haldane ever since. Throughout the book, he strives to relate Haldane’s politics to today’s. Sometimes this makes for a rather didactic approach. I was lost in the chapter on Haldane’s idealist philosophy (though that may be my fault rather than the author’s). He drills down into Haldane’s policymaking in areas such as education, army reform and the federal constitution of Canada, and we occasionally lose sight of Edwardian political culture.

Campbell has succeeded in his aim of writing a biography of Haldane which might serve as a handbook of leadership and statesmanship in this post-Brexit age. However, the figure that came to mind as I read about this huge, endearing, vulnerable man was not a sleek and shallow modern politician but Babar the elephant, who, like Haldane, belonged to a species threatened with extinction.