And he should know as his Golders Green home is full of, among other collectibles, thousands of pieces of antisemitic material.

Why should a proud Jew and loyal Zionist be obsessed with collecting antisemitic material?

Dr Cohen is not really sure. His strange habit developed gradually.

The son of a London GP, boasting a daughter gynaecologist, nephews who are a cardiologist and a paediatrician, and a cousin who is a Jerusalem professor of medicine, Dr Cohen grew up with the normal childhood hobbies of stamp and coin collecting.

But he discarded these pastimes when he began to study medicine.

The Golders Green Synagogue member is proud that his three daughters and their families are all Shabbat observant.

His Jewish commitment also developed gradually.

He said: "My parents wanted me to be a Jewish gentleman and sent me to the City of London School, a well-known public school with a heavy Jewish following.

"I thought of going to yeshiva when I was about 14, but nobody did in those days. The biggest thing was to be English. Anglo-Jews used to play with religion.

"My parents were kosher, certainly at home and more or less outside. My father was the shul warden, but my parents were not particularly Zionist.

"People were not, when I was growing up. My parents thought Israel was a place for refugees.

"But my family has become a lot more observant. Nowadays you go one way or the other. The whole Jewish issue has become much more central.

"Most of the children of my friends from my misspent youth are married out. But all my kids keep Shabbat."

Dr Cohen's now ardent Zionism must have been helped by the fact that he married an Israeli.

His wife Yael, whom he met at London's Hillel House when she was a postgraduate art student, later became a Jewish Care art therapist.

They married two weeks before the Yom Kippur War, after which Dr Cohen volunteered at Tel Aviv hospitals.

Dr Cohen left school at 17 and qualified in medicine at 21.

"I was a bit doubtful about medicine," he claimed. "I didn't really work very hard.

"In my first year I nearly came top of the class. I realised it was very easy to get through medical school. In fact I took a full-time job, not that I needed it financially.

"I wanted to see what being a stockbroker was like. That didn't last. I went back to medicine."

But his real passion turned out to be collecting.

He said: "I was a stamp and coin collector as a kid. I liked old things and the odd old book. I gave that up when I was a student and qualified. I didn't go back to collecting till after I was married."

At a loose end after the birth of his second child, Dr Cohen went on a fishing trip, where he met someone who collected maps. The doctor decided to follow suit, specialising in old maps and atlases of Israel and Palestine.

He said: "The first things I collected were often written by missionaries. I started with non-Jewish books with maps of Israel and atlases.

"I went to fairs, got to know dealers and bought stuff from them. I enjoy the hunt for things. When I go to conferences around the world, I am always on the lookout for collectibles.

"A lot of fairs take place on Sundays. A regular feature of my week is to go on a Sunday to fairs, mainly London, but I have travelled to York, Birmingham and the West Country, all over, whenever there's a fair and I have the time."

He admitted: "It's a very stupid way to spend your money. The collectibles may well end up being less valuable after a period of time, not like on the Antiques Roadshow. Things go out of fashion. You have to live long enough for them to come back in."

From maps of Israel and Palestine Dr Cohen progressed to postcards and children's books, particularly Jewish ones.

Hebrew alphabet charts, he says, go back 400 years and books 200, while Jewish storybooks began in the 1930s and 40s.

In 2002, the murder by terrorists in Israel of teenager Yoni Jesner, the brother of his son-in-law, Ari Jesner, left a profound impression on him.

He was determined to do his bit to counter the anti-Zionist and antisemitic propaganda, which fuelled the Intifada.

Around the same time, he met Dr Joel Kotek, of Belgium, who wrote the book Cartoons and Extremism - Israel and the Jews in Arab and Western Media.

Dr Cohen decided to collect antisemitic material.

"The whole idea is to show people how the same images have been recycled throughout time," he said.

Medieval antisemitic themes like the blood libel and a Jewish plot for world domination were still being used, not only in the Nazi era, but also in contemporary anti-Israel cartoons.

These included the cartoon of Ariel Sharon eating a baby, which won its creator, Dave Brown, political cartoon of the year in 2003.

Surprisingly, Dr Cohen said, even early 20th century Jews were capable of designing cartoons which looked as though they had come straight out of Der Sturmer.

He said: "Jews then had a very low self-image."

Dr Cohen has exhibited his collections at the European Parliament, the London Jewish Cultural Centre and in Jerusalem and Copenhagen.

He reckons he has more than 700 antisemitic postcards and hundreds of magazines and newspapers like Der Sturmer, as well as more recent examples from Palestinian school books about destroying Jews.

His oldest items are prints from the 1493 Nuremberg Chronicle, picturing the blood libel.

Ideally Dr Cohen would like to get rid of his collection of antisemitica, which he regards as "depressing", but he wants to make sure it doesn't get into the wrong hands.

He said: "There are people who ask why I have this stuff. I ask myself as well. I certainly would like to get rid of it. I'd like to see my collection used for educational purposes for non-Jews.

"The key message is about the recycling of propaganda, that the same messages are used by all antisemites. I am very concerned about the denigration of Israel and about antisemitism."