England in the 1870s: the age of steam, empire and geological hammers chipping away at faith. Yet it was also a time when spiritualism, cults and utopias flourished. In the heart of the New Forest, more than a hundred poor men and women lived together in a religious commune, led by a farm labourer's daughter who claimed to be the female Christ.

Mary Ann Girling had left husband and home proclaiming that the Second Coming was imminent and that she and her followers would never die. In exchange for immortality, the Children of God (or "Jumpers", as they were known, because of their ecstatic dancing) gave up sex, worldly possessions and their families. Village women, blacksmiths and cobblers followed Girling from Suffolk to London and on to a house in the New Forest, only to be evicted to the surrounding muddy fields as the cult descended into ever weirder rituals, near-starvation and death.

If Philip Hoare, biographer of people and places, had stuck with this tragedy, he might have been able to explore the issues he tantalisingly raises. What makes for the success or death of a cult? What dis-tinguishes the crazy prophetess from the respectable mystic? Instead, like the author of a medieval bestiary, he provides a wonderful catalogue of the weirder varieties of Victorian belief while forcing them into the framework of the New Forest. So he tells us about other extraordinary New Forest denizens: Andrew Peterson, a barrister guided by the spirit of Sir Christopher Wren, who was building a tower taller than Nelson's Column; and Sir William Cowper and his wife, who hosted seances attended by John Ruskin, desperate for contact with his dead love.

Yet the framework of the New Forest never quite holds. Hoare cannot resist darting off around America and England in pursuit of Ruskin, spiritualists and Girling's predecessors - witches, mystics, saints and madwomen. And although the spiritualist Cowpers supported their Jumper neighbours, they were worlds apart in class, wealth and respectability.

Hoare's New Forest is England's lost Eden - the site of vanished utopias and of a faith that no longer exists. "They all believed," he writes nostalgically, implying that this is what made them so different from us. But why? Hoare emphasises the capitalist harshness and uncertainties of the late 19th century, as if these made the Victorians particularly susceptible to cults. But hasn't every age felt itself to be living through uncertain times? Are those 19th-century Jumpers so different from the Branch Davidians of Waco? With their New Age-style festivals and Waggie, their personal homoeopathic clairvoyant, weren't the Cowpers really proto-hippies? Even the spiritualist credulity of Dickens, Tennyson and Gladstone should be familiar to us - think of the Blairs.

Given that Hoare likens the evictions of the Children of God to those of New Age travellers, it is surprising that he misses the parallels with the peace protesters at Greenham Common. Like the Greenham women, the Jumpers drew inspiration from the rural communitarian Diggers, and they, too, depended on the crowds who came to scoff or sympathise. Girling charged the public to attend her rituals, which often degenerated into chaos. Spectators would throw bags of flour, heckling the tall, thin Suffolk woman with her "high cheekbones and piercing eyes", or smacking their lips and shouting "Ain't it nice" as the Jumpers greeted each other with a kiss. As the dwindling group suffered repeated evictions, their makeshift homes also looked increasingly shambolic, the fields muddier, their costumes stranger, their behaviour more alien. But there was one major difference between the Girlingites and their Greenham counterparts: their sacrifice was for real. The listless women by the fire were literally dying of starvation and cold.

By now, Girling was calling herself God-woman; she bore the stigmata and dressed in white to herald the Second Coming. She was worshipped by her emaciated followers, 11 of whom died. Girling herself died of cancer of the womb in 1886. It is not surprising that the cult had unravelled: the poor and powerless cannot sustain an organisation; utopian communism does not pay the bills; and immortality is a dangerous selling point.

As for Hoare's spiritualists - poor Ruskin went mad and Cowper was ennobled. And Peterson's tower became a home to mobile-phone transmitters.