Lilburne would not have talked about "levelling". "Leveller" was an insult thrown at him by his Royalist and Parliamentarian enemies. He and his friends indignantly rejected the charge that "we would level all men's estates, that we would have no distinction of orders and dignities among men" as a malicious slander. Meanwhile, modern researchers wonder how seriously the Levellers believed in universal male suffrage - the main demands were for an end to rotten boroughs and for an English republic, not one man, one vote. As for feminism, Lilburne would never have dreamed of advocating "the levelling of women". Our notions of equality between the sexes were beyond the most radical minds of the 1640s.

Historical fact should not bind the writers of historical fiction, of course. But Channel 4's fiction is unintentionally fascinating because it relies on an interpretation of the Civil War that is at least 40 years out of date. From the late 19th century, the rise of the social democratic and socialist movements rescued the forgotten Levellers and the primitive communists of the Diggers movement from obscurity. As Blair Worden says in his Roundhead Reputations: The English Civil Wars and the Passions of Posterity, "once more the present saw its reflection in the past".

The 18th-century Whigs had drawn ideological succour from the parliamentarians' stand against the Crown but deplored the excesses of the revolution. Victorian liberals whitewashed the excesses and turned Cromwell into a plaster saint - a champion of liberty, worthy of a statue in Parliament Square. The mid-20th-century Left went further and argued that the revolution failed because it was not excessive enough. Cromwell and his greedy bourgeois allies destroyed its base by moving against the radical ideas of the Levellers and Diggers - a dampening of ardour that they were determined to resist in their lifetimes.

Students read the left-wing historians Christopher Hill and E.P. Thompson. Scratching around for a name, a group of folk-punk musicians decided to call themselves The Levellers. Not to be outdone, Billy Bragg outflanked them on the left and dedicated a song to Gerrard Winstanley, the Digger leader.

Worden stops his account of how successive generations used the past in the mid-1970s. It is a pity he did, because by then historians were beginning to realise that the russet-coated captains of the New Model Army were not always potential readers of the New Statesman. They grasped that men murdered each other, blew up churches and supported or opposed Cromwell's theocratic rule, not because religion was a cover for class or political interests, but because religious passions moved them above all others.