The day the working man first got to have his say in how England should be governed

The king was not yet dead. But he had been defeated in battle, and the way was open for the most radical debate in England's political history.

It began 360 years ago in the church of St Mary the Virgin, in the village of Putney, six miles south-west of Westminster, where today a week of celebrations begin to mark one of the seminal events in the history of democracy – the occasion on which ordinary people established the principle of votes for all.

As Gordon Brown launches his nationwide consultation on a British bill of rights, possibly leading to a written constitution, he could do worse than begin with Putney. There, in 1647, leading members of the anti-monarchy forces in the Civil War met to debate the future of England. "It proved," says the historian Tristram Hunt, "to be one of the greatest intellectual encounters in Western political thought." It shaped the development of democracy in not just Britain but throughout much of the world.

Yet credit was long not given to the pivotal role of the Putney Debates. Uniquely, a verbatim record of what was said was preserved, thanks to shorthand notes taken by the army secretary, William Clarke. But so explosive were their contents that they were not transcribed for more than a decade and then hidden away in the library of Worcester College, Oxford, where they were found only in 1890.

Members of the New Model army gathered to debate the future shape of the nation's constitution. Should they negotiate a settlement with the defeated King Charles I? Or should they do away with not just the King but the bishops and House of Lords?

There were two sides to the debate, which Cromwell chaired. The conservatives were the parliamentary gentry known as the Grandees. The radicals were the Agitators, elected representatives of the rank-and-file soldiery, whom their opponents called Levellers – the first time the voice of the common man had been heard in English politics.

Radicalism was in the air. One in 10 Englishmen had died in the war. That "man of blood" King Charles, all agreed, could never again be allowed to exercise arbitrary sovereignty under the guise of a divine right of kings. But the Grandees wanted him checked by a parliament in which only property-owners could vote.

The ordinary soldiers sniffed betrayal about. Many Grandees wanted to ease the tax burden by disbanding the troops without the back-pay many were owed. Levellers like John Lilburne had already scornfully attacked the Grandees, saying witheringly "all you intended when you set us afighting was merely to unhorse and dismount our old riders and tyrants, so that you might get up and ride in their stead."

In late October 1647 the Agitators presented their commanders with a document, the Agreement of the People, proposing widespread constitutional change. It was a defining document. It demanded equality before the law, freedom of religion and of speech, an end to conscription, a parliament elected by every man in the country (with a two-year fixed term and equal sized constituencies) over which neither King nor Lords would have any sway.

In a passionate speech, Colonel Thomas Rainsborough, the highest-ranking officer to support the common solders, said: "Every man that is to live under a government ought first by his own consent to put himself under that government". That meant every man should have the vote.

The Grandees were horrified by this spectre of egalitarian democracy. It would bring anarchy. It would bring corruption as rich politicians bought the votes of the uneducated masses. The debate was highly religious, preceded once by five hours of prayer, with both sides citing biblical and theological justifications. Almost all were Puritans but a key group known as Independents insisted on freedom of conscience and worship. No one, they said, should be compelled to attend church or hold particular beliefs. "The story of British democracy is intimately bound up with the theology of Protestant Christianity," says Tristram Hunt.

Over the week that followed, the ideological chasm between the two sides remained undiminished. The crafty Cromwell tried a variety of tactics (which modern-day politicians would recognise) to divide the opposition, insisting he was "not wedded and glued to forms of government", calling for unity, suggesting passing the issue over to a committee. But on 4 November, in defiance of Cromwell, the Army Council voted to extend the franchise to all men, except servants.

It was a short-lived victory. A fortnight later, when the Agitators turned up to a meeting of the whole army, Cromwell had them put to the sword. Subsequent mutinies were crushed with equal ruthlessness.

But if Levellers and their allies failed in the short term, eventually almost all they wanted came to pass. Some of them boarded the Mayflower and acted out the new democracy in America.

In England, their dreams came more slowly to fruition. Cromwell began the process. Other Leveller desiderata were embodied in the Toleration Act of 1689. As the centuries passed the franchise was extended, with every man gaining the vote just six years before the transcripts were found in 1890. From those proceedings in Putney issued forth ideas that were to be enshrined centuries later in the Universal Declaration of Human Rights.

They were not written in the calm of a lawyer's chamber in a time of peace. They were hammered out, in debate, in a time of crisis. Yet they paved the way for many of the civil liberties we cherish today, some of which – like trial by jury and no detention without trial – are today again under threat in the face of the violence in our own age. The Putney Debates are a timely reminder that that our freedoms were hard fought for. They should not be surrendered lightly.