A very British crusade

In the summer of 1782 the British-owned slave-ship Zong, crossing the Atlantic from Africa to Jamaica under Captain Luke Collingwood, got hopelessly lost. After three months, 60 of the 440 slaves on board had died, with potentially disastrous consequences for Collingwood's prospective bonus on the profits from the cargo's sale.

So he hit upon an insurance scam whereby his crew threw no fewer than 132 of the sickest slaves overboard to drown - still shackled if they put up any resistance - and he claimed to the insurers that he had been forced to do it because of dwindling water supplies.

Had it not been for the moral qualms of the chief mate, James Kelsal, who revealed that there had still been 420 gallons of water on board when they had reached Black River Port in Jamaica a month later, Collingwood would have got away with it.

As it was, neither he nor anyone else was ever indicted for the murders, and the case went first to trial and then appeal solely as an issue of civil insurance fraud. It was hardly covered in the press at the time, and for five years anyone who brought up the scandal was considered a bit of a crank.

Then on 22 May 1787, 12 men met in the print shop of a Quaker, James Phillip, in George Yard in London. Each was deeply religious, nine of them Quakers although the two leaders, Granville Sharp and Thomas Clarkson, were Anglicans. They were all outraged by the story of the Zong, and that day they pledged themselves to do something utterly revolutionary - abolish slavery throughout the British Empire.

Adam Hochschild's fascinating, well-researched and well-written book is about how they accomplished that remarkable goal half a century later. Slavery had built the greatest civilisations of the ancient world - Egypt, Greece and Rome. It was considered an inevitable part of the human condition by thinkers as wise as Aristotle, Sir Thomas More and Adam Smith.

The political philosopher John Locke owned £600 of stock in the Royal African Company; America's founding father Thomas Jefferson owned scores of slaves, Voltaire agreed to have a slave-ship named after him, and the Church of England itself owned the 710-acre Codrington slave plantation on Barbados (where appalling brutality was commonplace).

Perhaps even more pertinently, many British parliamentarians of both houses in 1787 enjoyed large incomes derived from the trade; the Lord Mayor of London owned 2,000 slaves; and slavery represented a large proportion of the then vibrant British economy, bringing employment to thousands of domestic shipbuilders, merchants and sailors.

It was also assumed that the British West Indian colonies simply could not function without it. "It is impossible for a man to make sugar without the assistance of Negroes," wrote the planter John Pinney from the island of Nevis, "as to make bricks without straw."

Yet by 1838 the entire institution was abolished throughout the British Empire, although it took another quarter of a century and a horrific civil war to destroy it in America, and Brazil's 1.5 million slaves and Cuba's 400,000 were not freed for half a century.