A contributor to the BBC's compelling new documentary series Jews talks in its second episode of the curious gaps in her family's history. Her mother coped with her own mother's death in a Nazi concentration camp by, she thinks, “obliterating” the past, trying to forget it happened. But Nicola Diamond adds a warning. “When you try to obliterate the past it doesn't actually go away. It comes back in states of anxiety that you might not understand.”

It was after interviewing around 100 Jews with similar family stories, many of them horrendous, that the film-maker Vanessa Engle was unexpectedly confronted with the truth of Diamond's observation. One morning she was forced to take her children to school by a route that entailed a Tube journey from King's Cross in London. When they arrived, the rush-hour crowd was so great that the gates had been closed and a guard was processing commuters through one by one. “In my head I was aware that I was thinking, 'If I pretend they're not mine, then they might send them to the same camp with me.' It was King's Cross in 2007. What is that? It's a terrible thing to find yourself thinking.”

The process of research had, she realised, taken her to a “dark place”. It was, however, one she had chosen, or been compelled, to visit. Over coffee in a Central London café, Engle, whose previous series include Art & the 60s and Lefties, admits she chose her latest subject because in middle age her family identity was becoming important to her.

“But that's a terrible answer because that's not a reason for anyone else to watch it.”

It is, however, a pretty good reason for wanting to make it, especially if, like Engle, you are one of a handful of documentary-makers still allowed their head within the BBC. Both Engle's mother and grandmother fled Germany at the end of 1938. Neither talked about the Holocaust. “There is a phenomenon of people arriving and feeling that they wanted absolutely to put the past behind them and their best chance for producing successful, unimpeded offspring was to not speak about it. And actually what's interesting in that film - it only struck me after I'd watched it a couple of times myself - was that actually all the children in that film became middle class again within a generation.”

Engle is 45, has curly black hair and pale skin. She is married to a man whose father was Jewish. On the programmes, however, she mentions she is Jewish only once, in a brief response to a question from an orthodox Jew. Growing up, she says, she felt it would be “sexier and more glamorous to be able to say, 'I'm Spanish, or I'm half Egyptian.'” Jewishness had “a slightly negative connotation”. The Next Generation, the central pillar of her trilogy of films, addresses what turns out to be a common feeling among second-generation British Jews. In contrast, the two films that flank it examine the determination of others to maintain their identity at a time when their Chief Rabbi needed to write a book titled, Will We Have Jewish Grandchildren?

The first film, The Prisoner, achieves rare access to the hermetic, media-shy community of Hassidic Jews in Stamford Hill, North London. It then pulls off another coup by finding within it a conflicted black sheep. The ultra-orthodox rebel is Samuel Leibowitz, who served nine years in prison in three different countries for drug smuggling. He returns to Stamford Hill not half as surprised as the viewer to find his old community strenuous in its efforts to reassimilate him. The title of the film suggests that he may be a prisoner still, this time of his community, and the documentary ends with him dreaming of escape.

“But he's still there,” Engle points out. “I suppose it's looking at what it means to be in what, to secular people, seems like a very repressive society, and is that a prison or isn't it? A few people have seen the film now, and a lot of people are overwhelmed by how positive that community appears. I think because we're all overburdened with choices and a lot of people have messed-up lives and divorces and children who are drug addicts or whatever it is, that people look quite longingly actually at those high walls and that clarity.”

Her final film, Keeping the Faith, is an observational documentary about the extraordinary Jonathan Faith, the former owner of the high street chain Faith Shoes, who in his early retirement is using marketing techniques and huge amounts of his own fortune to persuade - or bribe - the coming generation to become orthodox. Despite his best efforts, it ends with him wondering if, with Anglo-Jewry having fallen from 450,000 in 1950 to 270,000 today, he is not fighting a losing battle.

“I think he was having a bad day that day. And he's still absolutely committed and carrying on,” Engle says, clearly a fan. “I guess we all have bad days.”

I ask if there is a comparison here with her previous series on defunct Sixties art movements and radical politics. “It hadn't struck me,” she says, surprised. “They're very contemporary films, because that whole question of what Jewishness is is very ‘now'; as is what it means to be religious now and how a community like the one in Stamford Hill can exist in the present age.” That community is in fact growing in strength, “because they are such good breeders”.

So, by the end of the series, did she feel better about being Jewish? “I felt much better about being Jewish. I did. I really did. When I embark on these things, it's a journey and you don't know where you might end up. I didn't feel that I was about to become religious and I'm still a firm atheist. But the worlds I'd seen were so rich and interesting and thought-provoking and I'd met so many people I admired and who had solutions to things that we don't have, that, yes, I did feel much better.”

Jews: The Prisoner, Wed, BBC Four, 9pm

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