The carving of Pakistan out of British India set off ethnic killings that cost about a million lives. It eventually led to today's dangerous nuclear stand-off between India and Pakistan. The latter has also been called the "epicentre" of Islamic terrorism - the country where Islamic extremism has a vast following and where its militants have received training on a large scale, as well as the arms, money and inspiration for their attacks abroad. And Pakistan's location as a vast Muslim country abutting the oil-bearing Middle East, Central Asia and China gives it first-rate strategic importance. Whoever set up Pakistan did something of tremendous consequence.

What was the extent of British responsibility? Historians argue about this interminably. Some say the British caused India's partition by fomenting Hindu-Muslim hatreds to prolong their rule in India. Others blame partition on Muslim determination and the nationalist Congress Party's failure to concede enough to the Muslims. The idea that this book by Narendra Singh Sarila, a retired Indian diplomat who was once an aide-de-camp to Lord Mountbatten, the last British Viceroy, should throw new light on Britain's role - as is claimed on its jacket - seemed highly unlikely. Yet the text fully justifies the claim. It is a valuable, highly readable, indeed fascinating study, that draws on recently released British documents. Sarila, who is full of rare common sense, explains things that have long been puzzling about British actions and attitudes.

The central figure is Lord Wavell, the penultimate Viceroy. One cannot read Sarila without concluding that Wavell was the most important British personality in India in the 20th century. Many historians see him as a dour soldier, intellectually accepting that British rule was about to end yet openly contemptuous of, and aloof from, the Indian nationalists. Historians often attribute the failure of British attempts to find a way out of the Hindu-Muslim political impasse partly to Wavell's inflexibility and inability to win Indian leaders' goodwill. Clement Attlee's Labour Government certainly took this view when it replaced Wavell with the infinitely more personable Mountbatten before Wavell's term in office was over. Other writers - notably Patrick French in his account of India's partition - see Wavell as a quiet yet sensitive man doing his best to save India's luckless millions from mass blood-letting but stymied by intractable Indian politicians and ill-informed masters in Whitehall.

Sarila's Wavell is startlingly different. Rather than being limited, he was far-sighted, but in a disturbing way. He would be thoroughly at home in today's feverish discussions of the strategic implications of Middle East events. The fate of India's hapless millions was far from being his main concern. He was a bleak realist, embodying the central and enduring British consideration in the whole matter: ensuring that leaving India did not endanger Britain's strategic position, especially in the Middle East and vis-¨¤-vis the Soviet Union.

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By the early 1940s, it was clear to the British that an India under Congress would not co-operate militarily with them, but that a part of India led by the Muslim League - Pakistan - was likely to do so. And Pakistan would include the really important bit of India from the viewpoint of British strategic interests: the northwestern part that bordered the Middle East. No wonder the British and the Muslim League forged such a durable alliance in the transfer of power negotiations. No other historian, as far as I know, has analysed the partition thoroughly from this perspective, whose importance is so obvious once it is pointed out. The centrality of the strategic motive is no mere speculation; Sarila validates it powerfully with quotations from British documents.

This way of looking explains some key British attitudes. Sarila may be going too far in suggesting that the British were consciously insincere in their claims to be seeking Indian unity. It may have been a severe case of divided purpose. Yet the facts are troubling. Why, for instance, should Wavell have been so adamant that only the Muslim League should represent the Muslims at the 1945 Simla Conference, when the league's support among Muslims was less than overwhelming? Such favouritism, protested against by the Governor of the Punjab, helped the league to eclipse its Muslim rivals, as Sarila points out. Again, Wavell kept warning London not to disregard Muslim separatism because the Muslim population was so big that this would cause terrible disorders. However, his own director of intelligence, as well as the Governor of the Punjab, had made it clear that a partition would bring enormous bloodshed.

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Yet the British are by no means the only culprits. Sarila is harsh on the Congress leaders, particularly Gandhi, whose deadly bungling bears as much blame for the partition as anything else. Gandhi's reckless 1942 "Quit India" campaign, a seriously disruptive rising against the British when they were fighting desperately to prevent a Japanese invasion of India, is a case in point. No wonder the British took such a grim view of the Congress after 1942. Damningly, no Congress Party leader tried to sound out the strategic concerns of the British and assure them that these would be protected in a united, Congress-led India.

Britain had its reward. For several decades, Pakistan became a crucial anti-Soviet ally of the West. But now it is perhaps America's and Britain's worst strategic nightmare, a place from which terrorism and nuclear weapons technology are exported, and closely allied with the chief future rival of the West: China. Perhaps it would have been wiser, when leaving a century-and-a-half-old empire, to think more about its inhabitants' fate than Middle Eastern strategy.

Radhakrishnan Nayar is a writer on international affairs.