Understudy in Downing Street

Lord Melbourne 1779-1848 by L G Mitchell, OUP, pounds 25; Amanda Foreman on the prime minister who fell from grace with Queen Victoria

When John Major became prime minister, one commentator likened him to Mr Pooter wandering into Downing Street by mistake. Melbourne's accession to power, after a scant six years as a minister, excited similar incredulity. He was a political nobody, without an ounce of charisma or drive. Metternich scathingly dismissed him as Charles Grey's "understudy". But the understudy played the role of prime minister, night after night, for seven years. How a man who was an acknowledged human failure could be such a success is one of the many, intriguing issues explored in L G Mitchell's Lord Melbourne 1779-1848.

This latest biography is a revelation in two senses. It reveals a darker, much more complicated man than the urbane aristocrat of previous studies. Second, it proves that academic history in the hands of a first-rate historian is never boring.

Lord Melbourne was irreplaceable for most of his tenure. Only someone as politically unobjectionable could hold together a Cabinet divided into Whigs, Radicals and Irishmen. Unfortunately, that Melbourne incited no great feeling underlined his uninspiring and hopeless leadership when bold action was required. His enemies accused him of "lounging" his way through politics. This was not strictly true. Melbourne was not lazy, merely passive. Whereas team captains usually want to win, the best outcome in Melbourne's point of view was a draw. When the Whigs were turfed out of government in 1841, he cheerfully remarked it was no great surprise: "We've always been losing since '33."

Ironically, for a man who disliked fuss, he had an uncanny ability to attract notoriety. Melbourne's private life was alternatively chaotic and tragic. His marriage to Lady Caroline Lamb was a 22-year exercise in public humiliation. She was an exhibitionist who relished publicising the most intimate details about her life, particularly her affair with Lord Byron. She was also a spoilt, insecure fantasist. But, Mitchell argues, their marriage was a folie a deux. Far from exonerating him, he suggests that Melbourne used Caroline as a kind of emotional proxy. There is some evidence that he beat her and that they indulged in games of ritual humiliation.

Mitchell has also unearthed extraordinary letters which show Melbourne expressing an unhealthy interest in corporal punishment. He was excited by flagellation and regularly used to thrash his child wards. "Well cocky, does it smart still?" one of them recalled being asked, after a long whipping.

After Caroline died, Melbourne continued to be dogged by scandal. He was cited in two embarrassing divorce cases. Even his quite innocent relationship with Queen Victoria fuelled gossip because of its intensity. The 18-year- old queen couldn't go to Ascot without spectators mischievously chanting "Mrs Melbourne".

In his two-volume study, David Cecil simply ignored those facts about Melbourne he didn't like. Philip Ziegler, on the other hand, condemned him outright as a man with "ice in his veins". Mitchell's humane biography provides a more balanced portrait of a diffident man whose personality and politics were deformed by his marriage. According to Mitchell, Caroline's betrayals left Melbourne scarred for life. Emotional responses were beyond him: "He could not join others, cope with others, accept others, or perhaps, love others."

Melbourne's fear of intimacy also made itself felt in his dislike of innovation. Ideas and strong policies required engagement and commitment. When he finally did summon the courage to make himself vulnerable again, to Queen Victoria, he enjoyed the happiest three years of his life. He adored her as the daughter he had never had; in turn, she worshipped him as a father-figure, mentor, and first love rolled into one. Sadly, he never recovered from the way she dropped him once she married Prince Albert. Visitors to Brocket Hall, where Melbourne spent his last days, were startled to find that the mere mention of her name caused tears to roll down the old man's cheeks.

Lord Melbourne is both absolutely uncompromising and utterly compelling. It is full of the most elegant, witty remarks, recalling a bygone era when stylish historical writing was prized among academics. There is something 18th-century about Mitchell's prose. Describing Melbourne's detachment from his Whig colleagues, he says that "Party, perhaps like a wife or a clinging mistress, closed options, made demands, and was generally noisy and tiresome". Melbourne may have inspired indifference among his peers, but Lord Melbourne will be an inspiration to historians.