Platt’s new book aims to dispel the myths surrounding the conflict, presenting its events as the result of doubt, misapprehension and mistakes made by the central figures involved.

The conflict itself was so limited that the epithet “opium war” was hardly deserved. The main battle, in Dinghai, on the island of Chusan (now known as Zhoushan), in Zhejiang province, was over in just 10 minutes. Chinese guns, one of the best of which “bore an inscription showing it had been cast in the year 1601”, were no match for modern British ships and weaponry. The aggressor’s “sixteen men-of-war (the three largest carrying seventy-four guns each), four steamers, and four thousand British and Indian troops on seven transport steamers” met no serious military resistance in a country whose population numbered 300 million people (one-third of the world’s population at the time) but was beset by internal conflict and economic strife.

Imperial Twilight is a fast-paced narrative of trade, exploration, diplomatic disputes and early cultural inter­action. The story of British efforts to enter China is fascinating and richly described.

First came Lord Macartney, sent to China in 1792 on Britain’s earliest diplomatic and trade mission, and received with famous disdain by Emperor Qianlong, who announced: “The products of our empire are abun­dant, and there is nothing we do not have.”

Then there was Thomas Manning, a Norfolk man obsessed with the idea of exploring China. After failing to enter the country through Canton, in 1810, he travelled to Bengal, in eastern India, from where he rode on horseback through Bhutan and into Tibet, becoming the first Englishman to enter Lhasa.

Robert Morrison (1782-1834) was a Protestant missionary who also found he was unable to enter China. Instead, he studied Mandarin and Cantonese, translating the Bible and writing the first Chinese-English dictionary at a time when the Chinese were forbidden, on pain of death, to teach their language to foreigners. Morrison converted only a dozen or so Chinese, but his translations paved the way for those who followed.

Imperial Twilight is stuffed with intriguing titbits: the captain of the HMS St Albans, which visited China in 1809 while carrying silver to Madras (now Chennai), was a brother of author Jane Austen; British and American expatriates in Canton enjoyed games of leapfrog, “played at all hours by fully grown men”; and traders, with war imminent and ordered to leave Canton, took with them all that was imp­ortant, “along with certain less necessary items, like the 524 bottles of wine one partner in Russell & Co. managed to salvage”.

On the Chinese side, Platt describes an empire beset by misfortune and bad policy. Revolts against authoritarian rule and official corruption had split the country, the peasantry was impoverished and silver flooded overseas illegally in exchange for opium and other goods.

The piracy that had plagued the coast during the 17th century had led the authorities to force peasants to move 15km inland; a policy intended to deny raiders supplies but that also ensured the coastline was left defenceless.

Various responses to the opium epidemic are also detailed. Corrupt officials profited from both the trade and attempts to enforce laws against consumption. Some advocated banning foreign trade, others the legalisation of opium, some the development of Chinese opium (Indian opium being widely sought for its superior quality).

The course of action taken by the Qing emperor Daoguang was to end harsh punishment for opium users and instead crack down on the trade in Canton, setting in motion the wheels of war. British official Charles Elliot panicked and prematurely declared the cession of Hong Kong Island to the United Kingdom while imperial commissioner Lin Zexu, charged with obliterating the trade, himself heightened tensions by destroying confis­cated opium and offering only pennies to the pound in compensation.

Platt’s endeavour, as he announces at the outset, is to understand “not how Britain won, for that was never in serious doubt […] Rather, the central question is a moral one: how Britain could have come to fight such a war in China in the first place”.

As such, his focus is somewhat skewed. While he details the complex forces that drove Britain to war, this often comes at the expense of the Chinese perspective. It is an imbalance that makes the book’s title something of a misnomer.

On the brink of hostilities, for instance, 10 pages are devoted to a debate in the British parliament – undoubtedly important, the vote to pursue an armed resolution was passed by the narrowest of margins, 271 to 262 – while just two paragraphs detail the policy of Emperor Daoguang. The book’s most belligerent figures are found in the British traders who seek to open up China while its most concilia­tory are members of the British government eager not to jeopar­dise the wealth generated by the China trade.

But what Imperial Twilight might lack in balance, it makes up for in the verve and relish with which its almost always readable, enjoyable and informative story is told.