It’s past 10pm, but work has just begun for the group of vigilantes in a small white hatchback patrolling the streets of Pisgat Ze’ev — a Jewish settlement on the outskirts of east Jerusalem.

As the car crawls through the nearly empty streets, the men peer out at couples. They say they are experts at spotting those that don’t “match”.

“Stop, right there. Stop the car. Is he an Arab? That dark guy . . . If they are both Jewish, keep the car moving!” yells out ‘David’, a 31-year-old Jewish settler who does not use his real name.

For more than a decade, David has considered it his unofficial job to patrol the streets looking for mixed Arab-Jewish couples. “We are protecting the Jewish people, our traditions, our heritage. Some people just get mixed up. We talk to them, explain why it’s important for Jews to be with Jews,” he said.

His group, which works with police, goes by several names, including Fire for Judaism, is composed of up to 45 men and funded by private donations. Members say they are fighting a “growing epidemic” of Arab-Jewish dating and spend as many hours as they can on patrol.

Similar groups have formed across the country, including in the southern Negev city of Beersheba, and northern port of Haifa. In Petah Tikva, a blue-collar city in the centre of Israel, the municipality has formed a unit to discourage Arab-Jewish relationships.

In Pisgat Ze’ev, the growing number of Arab-Jewish couples is seen as the result of more Jewish settlements in Arab east Jerusalem.

“The problem is always with Jewish girls dating Arab men. The Arab guy comes and buys them things, treats them well. They fall for it. They can’t see what they are doing,” says David.

Sarah, who asked not to use her real name, said it is men like David who are the problem, not her Arab boyfriend, Zadar. “I’m not stupid, or gullible or looking for trouble. I’m a Jewish girl who happened to meet a guy I like, who happens to be Arab. It’s my business. We have to go other places to go on dates, places where these guys won’t find us,” she said.

In Petah Tikva, municipal workers said they only sought out under-age Arab-Jewish couples when asked to intervene by parents. “This is not a racist thing. Statistically, these girls wind up in trouble. We try to step in before real harm can be done by talking to the teens, making social workers available to them. We never use force,” a spokesman said.

David says that he too, will not use force but on a recent night out, it became clear that he was prepared to do just about anything else. At the start of his patrol he caught sight of a “known problem couple”. It was a young woman, stepping into a vehicle that he said was full of Arab men.

A car chase ensued through the windy mountain roads before the vehicle got away. David took down a licence plate number and called in the incident to the police. “I am doing this for her own good. She doesn’t know what she is getting into. It’s not like these guys are offering her a future.”

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