If we were to pick a spot where it all began, it would be a Quaker bookstore and printing shop at 2 George Yard, a small courtyard in the City of London. George Yard is still there today, but in it you will find no monument, no plaque, no troops of visiting schoolchildren — only the service entrance to an office tower.

The building that once stood here was a bookstore and printing shop. The proprietor was James Phillips, publisher and printer for Britain's small community of Quakers. On the late afternoon of May 22, 1787, after the pressmen and typesetters had gone home for the day, 12 men filed through his doors. They formed themselves into a committee with what must have seemed to their fellow Londoners a hopelessly idealistic and impractical aim: ending first the slave trade and then slavery itself in the most powerful empire on Earth.

Because Britain so dominated the Atlantic slave trade, starting an antislavery movement in Britain in 1787 was as Utopian a task as it would be to start a renewable energy movement in Saudi Arabia today.

The minutes of that historic meeting, in the clear, flowing handwriting of the committee's firebrand travelling organiser, Thomas Clarkson, begin simply,

'At a Meeting held for the Purpose of taking the Slave Trade into consideration, it was resolved that the said Trade was both impolitick and unjust.'

Throughout history, of course, slaves and other oppressed people have periodically staged uprisings. But what made the movement that grew out of the George Yard meeting so unprecedented was this: It was the first time that a large number of people in one country became outraged — and remained so for many years — over the plight of other people, of another colour, in other parts of the world. In a way, all modern movements for social justice spring from this moment.

The movement took off immediately, in a way that earlier scattered efforts never had. Petitions flooded Parliament, which the following year took the timid first step of regulating conditions on slave ships. Slavery became the prime topic of the London debating societies.

In a seven-year period, Clarkson rode 35,000 miles by horseback throughout England, Scotland and Wales, setting up local antislavery committees. Remarkably for the time, these committees were interdenominational: they included both the determinedly antislavery Quakers and people from other religious sects as well.

No one was more astonished than the powerful slave owners' lobby, which previously had only concerned itself with sugar tariffs and the like.

'The Press teems with pamphlets upon this subject, and my table is covered with them,' Stephen Fuller, London agent for the Jamaican planters, reported in despair to his employers.

One reason the abolitionist campaigners were so successful was that they were imaginative in finding new ways to carry their message to the public. In addition to the traditional tools of books, pamphlets and collecting signatures on petitions to Parliament, they boldly seized on what might be called the 'new media' of the day.

In 1788, a local antislavery committee in Plymouth created a diagram of a slave ship, based on a real ship, the Brookes of Liverpool, showing how slaves’ bodies were packed below decks like sardines. You have probably seen this now-famous image.

As soon as the London committee realised what a powerful tool it was, they ran off 8,000 copies and put them up in pubs all over England. A new member of the committee, the pottery entrepreneur Josiah Wedgwood, created a seal for the movement—a kneeling slave in chains, surrounded by the legend, 'Am I Not a Man and a Brother?' It rapidly appeared on coat buttons, hatpins, and women’s jewelry, and was probably the first logo every specifically designed for a political movement.

The very idea of a national committee agitating for a cause, with its headquarters in the nation’s capital, in communication with local chapters in cities around the country, was a relatively new one, and it had never previously been done in so sophisticated a way. Today almost every organisation, working on any issue from the war in Iraq to hunger in Africa, uses the same model.

In 1791, the movement developed a new tactic: hundreds of thousands of people began boycotting West Indian sugar, the principal product grown by slaves.

This was the first widespread, well-organised consumer boycott—another tool we still use today. It was an especially important advance in political campaigning because the people making the decisions about what food to buy for a household were almost always women. At a time when women could not vote or hold public office, this was the first time large numbers British women made their voices heard politically.

Women were also important in a later phase of the movement. Inspired by an outspoken Quaker pamphleteer, Elizabeth Heyrick, more than 70 women’s—or 'ladies', as they were then called - antislavery societies took root, and they were almost always more radical than those of the men.

Abolitionist campaigning reached a high point during and after the 1832 elections for Parliament. Lecturers toured the country talking to huge crowds, sometimes showing props like a slave whip. Activists published advertisements showing where candidates stood on slavery: for, against, or undecided. And the antislavery lobby staged mass meetings and a street demonstration, a march on 10 Downing Street.

At the same time, partly inspired by rumours of the organising going on in Britain itself, some 20,000 Jamaican slaves staged a huge uprising in 1831-32, the largest ever seen in British territory. The British army and the local militia suppressed it only with the greatest difficulty, and officials returning to Britain testified that they might have trouble doing so the next time. These events helped push Parliament, in 1833, to vote to emancipate the slaves.

No more chained slaves cross the Atlantic today, but the spirit that crystallised at that first meeting at George Yard is with us in a different way. In the idea that people everywhere who care about justice have the obligation to speak up for those denied it lies the birth of the vision that human rights are universal.

In this very unequal world of ours, where decisions made in one country — on subjects ranging from military intervention to globalisation to the global warming that affects us all— connect us morally to the farthest corners of the Earth, this is an idea that seems more relevant than ever. In that sense, the process born on that long-ago afternoon in 1787 is not only incomplete, it has barely begun.