Nazi extermination nearly made Hasidism extinct. When it revived, it was even more extreme. Hasids now make up over a tenth of the Jewish communities in Britain and Israel. A patchwork of ultra-Orthodox and Hasidic enclaves, many of them Yiddish-speaking, now covers a third of Jerusalem. Israeli Hasids have raised "modesty patrols" that harass women that displease them. Warning sirens announcing the Sabbath have been installed. These are not always peaceful people. Hasids throw stones, brawl with the police and agitate for men and women to be segregated on public transport.   

Extremist rabbis explain the Holocaust as "divine wrath". The old holy ways had been catastrophically deviated from. For the fury to abate, they decreed "true" Jews must speak Yiddish and refuse to learn "secular" subjects like mathematics. Then they must father as many children as possible. Devout Hasids must not work but study as long as possible in state-funded yeshivas (seminaries). Nor should they serve in the Israeli army. 

Uman has thrived on the fanaticisation of Hasidism. But it attracts every kind of fanatic. Nachman's Hasids splintered into a dozen warring courts. Some are breathtakingly pious. A few are riddled with child abuse and organised crime. Some offshoots wear all-white and are into marijuana and New Age trance music. Others, whose rabbis have Ivy League PhDs, are rigorously intellectual. Talk of Uman miracles and rumours of magical cures have spread throughout Israel, especially among the poor. My estimate is that Uman pilgrims are 90 per cent Israeli but only 70 per cent Hasidic. The remaining 30 per cent contains every imaginable Jew. They are mostly from Israel's Sephardi underclass: Moroccan cooks, Yemeni stallholders or Iraqi plumbers. But there are busloads from London and Paris and planeloads from New York. However, one kind of Jew is informally banned — women.

Uman has been called the Hasidic Mecca and the Hasidic Glastonbury. Overwhelmingly, the pilgrimage is rejected as "un-Jewish", even by other ultra-Orthodox Jews, because men abandon their wives and home rituals. Mainstream rabbis have accused it of escapism and even of "smacking of Christianity". Fringe blogs warn of Hasidic gay parties. Uman thrives regardless. 

I began packing. Uman, I thought, sounds like a nightmare. Twenty thousand exuberant Hasids taking off from Tel Aviv clapping their hands, heading back to Ukraine to flickeringly recreate a shtetl on soil filled with dead Jews. In transit, I checked Twitter for news. Overexcited Hasids had rioted before takeoff. Inexplicably they had hurled the drinks trolley at an El Al stewardess. 

I woke up in Uman. In a white knitted skullcap, a Talmudist from Barnet was rocking back and forth, bellowing Cockney-accented Hebrew. He had paid £750 for a week to rent a room in a mite-infested Brezhnevite apartment block without electricity, but with ripped wallpaper and cockroaches.