I expected to dislike this book. It is, after all, the book of a TV film, in which the youthful historian prances in front of the camera, exemplar of the "history as the new gardening" syndrome. Although widely recognised as a singularly clever and provocative fellow, Niall Ferguson is also a natural Scottish conservative, more like the New Statesman's house reactionary, John Lloyd, than a not-so-young fogey such as Andrew Roberts. So I was predisposed to write a hostile comment. Yet once you move beyond the coffee-table feel of this handsome production, with its spread of evocative pictures, you find a serious mind at work, with a century-old message: the British empire was about money and markets and capitalism. That's a good start, and worth arguing about.

It was a popular attitude at the beginning of the 20th century, and was once discussed fiercely in the 1950s and 1960s as the old imperial order collapsed. Was the empire a net gain or a net loss to its motherland? Later, when historians became economically illiterate, or non-numerate, they abandoned that argument and turned instead to "subaltern studies", concerning themselves with the role of the empire's underclass: soldiers, settlers, slaves and women.

Ferguson is intelligently numerate, a skilled financial historian by training and, although a gifted amateur in imperial history, he returns the empire debate to the economic track that was laid a century ago by the likes of Hobson, Brailsford and Lenin. In this attempt, he is less an incarnation of Arthur Bryant, whose mellifluous and ultra-reactionary version of history in the imperial heyday of Britain was popular in the 1930s, than of Eric Hobsbawm, but without the Marxism. Ferguson also lacks Hobsbawm's wonderful style and his encyclopaedic knowledge of culture and society.

Great British historians have been characterised by their capacity to write excellent English. If Ferguson is one day to grace that pantheon, he will have to burnish his prose. You can make coarse jokes to a television audience to jolly the viewers along, but the ordinary reader demands a text that is more persuasively argued and more attractively phrased.

In Our Empire Story, a book influential throughout the empire a century ago, Henrietta Marshall warned her readers that "the stories are not always bright", but suggested that they should "still love our Empire and its builders". The snag about Ferguson's book for a progressive readership, with its inherited tendency to believe that the empire was a "bad thing", is that he has come to believe, along with Marshall and his own Scottish forefathers, that it was a thoroughly "good thing", at least for Britain and the British (or perhaps one should say for Scotland and the Scots, as Ferguson gives us a Scottish view of empire). This argument might not earn you high marks in some of today's universities, though it would certainly raise a cheer in Downing Street - to whose attitude to empire Ferguson devotes a valuable coda. He thinks, more controversially, that the empire was good for the world, and that something like it might not be bad for the 21st century either (note to the Americans).

His book follows the six-part format of his Channel 4 television series, devoted to British exceptionalism, white migration, Christian missionaries, Victorian presumption, the power of the (Maxim) gun, and imperial liquidation. As befits an extended television show, he concentrates on a handful of archetypal "characters", but these are not always the ones expected. He also tells several unfamiliar tales.

Underpinning this enterprise is Ferguson's belief that the imperial experience, with slavery and gunboats and all, was good for humanity, not least because it "enhanced global welfare". Despite the charges of exploitation, racism and genocide (which he acknowledges but does not dwell on), he argues fearlessly that "no organisation in history has done more to promote the free movement of goods, capital and labour than the British empire in the 19th and early 20th centuries. And no organisation has done more to impose western norms of law, order and governance around the world."

This may well be true, and is worth discussing, but must we accept that it was a "good thing"? Such a congratulatory and Eurocentric view of the benefit of "western norms" has to be argued more fully than he is able to do within the confines of a television series. Ferguson is so fascinated by the world of finance and capital that he too often neglects or plays down the role of land and labour, those other significant economic variables. He delights in telling us that the American revolution was caused by tax cuts rather than tax hikes, but fails to take account of the more recent argument that it was about land. After the capture of Canada, the British handed over the entire hinterland of America to the Indians. They sought to stop the rapacious white settlers from moving endlessly westward, requesting them to finance the military force that would have prevented them from so doing. Small wonder these early enthusiasts for lebensraum rebelled.

This was the story of empire elsewhere, the people on the frontier disregarding the advice of the people back at base. Ferguson praises the British at home for maintaining a permanent critique of empire, but because no one took much notice of this opposition, it can hardly be advanced as a useful defence of the imperial project.

Strange, too, at the start of the 21st century, to find that he has little to say about Islam. In much of the empire for much of the time, an undeclared struggle against Muslims took place, yet this hardly features in Ferguson's story. He does follow John Buchan in noting the German enthusiasm for stirring up an Islamic jihad against the British, but barely mentions how Muslims were quite capable of organising one themselves. He hints that the British defeat by the Turks at Gallipoli may have had something to do with the "Islamic fervour" of the Turkish defenders, but does not return to the theme. Nor does he explain that the contested spread of muscular Christianity was not just into areas occupied by "savage tribes", but also into zones where Islam was well established.

Ferguson further argues, rather feebly, that the collapse of empire was the result of the clash of empires in the Second World War. This is not really sustainable, and he himself notes that the heroes of empire were already having severe doubts about the project in the 1920s, when the British empire itself was running out of money. In truth, the empire was in effect finished off by the First World War, which overextended its reach and taught its rebellious subject peoples to realise that they were not alone. Ferguson suggests that most of them, especially the Indians, supported the war effort. This is not so. When the Raja of Manipur raised a labour corps for service in France, it led to an uprising among the Kukis that was suppressed (in 1917) only with the help of the Assam Rifles. Similar mutinies occurred in East Africa.

The author concludes by asking why the United States has failed to pick up the white man's burden dropped by the British, and points to the differences. Whereas the British exported their capital and labour to the empire, the Americans have been net importers of capital in the past 30 years. The US, unlike Britain, has remained a nation of immigrants, rather than a promoter of emigration. The Americans seem content to use their aerial gunboats, and to sustain a rhetoric of promoting democracy and capitalism overseas; but they have always been reluctant practitioners of direct rule. Perhaps we should be thankful for small mercies.

Richard Gott is writing a book about imperial rebellions