Then the American-born rabbi, who goes round the world lecturing against Christian missionaries, received a request to talk to hundreds of Indonesian Christian pastors who claimed to be of Jewish descent.

The rabbi was told that the pastors were considering returning to their ancestral faith.

He told Elisheva Wiriaatmadja, the Indonesian would-be convert who had made the request: “Get me a ticket. I am on my way. This is a once-in-a-lifetime opportunity.”

When the rabbi arrived in Indonesia’s capital, Jakarta, he found nearly 500 Jews and would-be Jews from all over the massive country waiting to hear why they should not believe in Christianity.

At the end of the three-day speaking engagement, the audience stood up en-masse and sang Shalom Aleichem.

Now Rabbi Singer has settled in the mainly-Islamic country where he has established four shuls attended by Jews, would-be Jews and even Muslims attracted to the Jewish faith and the rabbi’s unique method of countering Christian missionary activity.

He explained: “In Indonesia there are thousands of hidden Jews. Around 15 years ago Indonesia was a very anti-Jewish country where you could not really practise Judaism.

“You had to identify on your national ID card as a religion, which was not Judaism.”

The reason was because during the Cold War era, Indonesian president Muhammad Suharto, who was supported by the Americans because he was very anti-communist, was also very anti-Jewish.

That situation has now improved to the extent that Jews can tick an ‘other’ religion box.

Rabbi Singer claims that antisemitism no longer exists in the vast, predominantly Muslim country, which is the world’s fourth largest.

He said: “Asians are not antisemitic, unlike in the UK and Europe where there are huge problems with antisemitism.

“South-East Asians don’t know what antisemitism is. People come over and kiss your hand. They have tremendous respect for Judaism and Jews. Everything is very benign in Indonesia. The Muslims are not Arabs. They are not really in tune with world politics.”

But because Judaism has not been a recognised religion in the country, thousands of Indonesian Jews assimilated into the church.

Among them are hidden Jews who went to West Papua, Indonesia, from Peru 400 years ago.

Their ancestors had escaped to Latin America from the Spanish Expulsion only to find Catholic persecution in Peru.

These hidden Jews had maintained some Jewish traditions and married only members of their own community, while converting to Christianity.

Thanks to Rabbi Singer many are now returning to their Jewish roots.

The enormous Indonesian archipelago is also home to Jews from China, Holland and Arab countries like Iraq and Yemen, as well as many Holocaust survivors, not to mention visiting business people and tourists.

Rabbi Singer said: “It is a big cholent. I am very happy that the Jews in the church come to my shuls so I can talk to them.

“I even have Muslims who are very interested in Judaism. I learn every Shabbat afternoon for a few hours and a lot of Muslims come. It is a different type of world.”

Rabbi Singer says that converting former Christians to Judaism is not his job.

He said: “I leave that to batei din in Australia or France or wherever. I wouldn’t dare.

“Rabbis in Muslim countries do not in any way engage in conversions. Former Christians are welcome to go America, Australia, England or anywhere.”

Rabbi Singer has established a mikva on the island.

Frozen kosher meat is brought in from the Philippines and New Zealand by visiting business people and many American products with OU kosher certification are available throughout Indonesia.

Despite his unusual approach to promoting Judaism, Rabbi Singer was raised in Brooklyn, New York, by a charedi family and attended the prestigious Mir Yeshiva.

He told me: “You are probably wondering how I got from Mir Yeshiva to helping Jews come out of the church.”

When he was around 17, he was shocked to see Jews for Jesus posters on display in Brooklyn.

Rabbi Singer said: “I was appalled that the church was still doing that in America. I couldn’t imagine why anyone would ever want to convert to Christianity.”

He realised that millions of Jews had become baptised by the church.

He said: “Their offspring are alive. They think they are Christian, but they are actually Jewish.

“I realised that my yeshiva education did not really prepare me to be able to answer all the questions. The missionaries were quoting from Christian literature and from parts of Tenach, which we didn’t really emphasise a lot in yeshiva.

“I quickly realised I had to really understand what they believed.”

So Rabbi Singer began to educate himself not only in Christian doctrines and the Tenach texts, which they interpreted to fit into their beliefs, but also in Islam and the Koran.

On holiday in Israel, he met a Christian missionary at the Western Wall. The rabbi spent his two week holiday with the missionary, who is now a rabbi in New York.

Rabbi Singer said: “That was a game-changer. He seemed like he was never going to leave the church. The firmer they project their beliefs, the more they assert they’ll never change, the easier it is to get them out.”

He said that a major technique was just to listen.

He said: “I realised that people get involved with missionaries for emotional reasons. Evangelicals are, for the most part, very nice people. Vulnerable people are looking for something spiritual.

“You have to listen carefully to what made them vulnerable in the first place and address those issues.

“I don’t say anything, I listen. I get what’s on their mind. I don’t want to come there with an agenda.”

He continued: “One thing my rebbe taught me when I was a child was that God gave us two ears and a mouth and we should try to maintain that ratio.”

But Rabbi Singer does a lot more than listen. He goes around the world talking about his anti-missionary work.

Beginning with a talk to the American women’s Zionist movement Hadassah, he began going around America talking about his work.

He has now extended that to speaking around the world. He has produced 500 YouTube videos on the subject as well as a two-volume encyclopaedic book.

His fame as a public speaker landed him with a show on New York’s Talk Radio station — one of the largest in America — and later on Arutz Sheva Israel National Radio talking about the Israeli political scene and how to counter anti-Israel propaganda.

More recently he began broadcasting on Fox News Radio.

But the station’s pro-Israel policy caused the rabbi problems with his Muslim supporters, whom he helps resist conversion to Christianity.

But in order to concentrate on the many Muslims who love to hear his talks, the rabbi is now limiting his input into Fox News to the subject of religion and not politics.

Rabbi Singer said: “I am one of very few rabbis who routinely speak in mosques not just for ecumenical reasons, for love and peace, but actually getting into the religion, the Koran.

“They really appreciate that and show an enormous amount of love for me.

“My agenda is to lessen antisemitism without compromising my support for Israel.

“Muslims know that I love Israel more than anything in the world. But because there is a rabbi defending Islam against the very serious charges made against them by Christians, they realise that all the antisemitism they learned in their madrassas is not true and that there are good Jews.”

He asked: “Is it worth me being on Fox News to risk everything I’d been doing with Muslims?”