Gary Hersham, otherwise known as the estate agent to the super-rich is the man that foreign buyers come to when they want to splash out millions of pounds on a Mayfair mansion. Diamond tycoon Lev Leviev and oligarch Roman Abramovich have him to thank for finding their London homes - and many other properties too.

So it is no surprise that last week I found him in a restless mood - anticipating an economic meltdown ahead of the European Union referendum vote.

By the time you read this you'll know if the Leave vote won the day. If so, Gary Hersham predicts mayhem. "The whole property world in England is going to be a disaster. The pound is going to collapse, the EU is going to not exist in a short while and I suspect there will be a global meltdown."

Whichever way the vote went, I have faith in his ability to weather the storm. He knows his clients very well: "At the super top-end nothing matters; perception can be turned into reality in seconds."

As managing director of Beauchamp Estates, which at any one time handles properties worth more than £1 billion, he is one of the most influential figures on the London property market.

He has two homes: one in Hampstead Garden Suburb, and the other not very far away in Belgravia. He's looking to buy in Israel, but "can't get the value right". He speaks seven languages (Arabic, German, Spanish, Italian, French, Hebrew and English) - a useful skill with his international client base.

Most of his friends are on the Sunday Times Rich List or in the public eye in one capacity or another. The morning we met, he had been chatting to property developer Vincent Tchenguiz, and had a meeting planned for later with Tory MP Zac Goldsmith. Those who know him best say he is deeply devout; a man who will never pick up a phone during Shabbat, an Orthodox Jew who is keen to support religious causes.

I want to know whether it is possible to fuse the three worlds - business, social and religious

- and if so, how has he managed to do it? I meet him at his office in Mayfair.

He's running 10 minutes late, so I walk around the reception past framed pictures of properties sold by his company. Beneath every picture are sale details. One frame reads (in neat calligraphy): "One Hyde Park, Knightsbridge, London, SW1. Sold by Beauchamp Estates, July 2011. £60,000,000 to £7,178 per sq ft." I learn later that his biggest deal was for £198 million, back in 1987. It's probably worth a billion today.

Hersham eventually walks in, flustered. Under one arm he carries a stack of papers; his 6am-9pm itinerary resting on top of the pile. He needs to be reminded that I'm from the JC. He also wants to know how much time this interview is going to take (I get 40 minutes).

He's best known for the 2014 BBC series, Under Offer. He showed viewers some of the biggest and most expensive properties in London, pointing out one client's full size model elephant in her Mayfair townhouse, as well as metres of indoor swimming pool, lavish gardens, marble floors and staircases swirling as high as Babel.

The owners are largely foreign buyers, but "up to 35 per cent are English", and Hersham, who has offices all over the globe, including Israel, says the majority of his business is done in London because "it is the safest place on earth".

He explains: "Flight of capital only comes to England. Nobody is going to come and take away your property like they do in so many parts of eastern Europe. You're going to be safe here, your family is going to be safe here. The worst that can happen to you is that the fiscality is going to be different."

What is it like to work with some of the biggest names in the world - and why do they go to him?

"I set this business up 40 years ago," says Hersham, 63, who recently returned from Miami having negotiated three trades to the total value of £1.4 billion. "A lot of my business comes because people know who we are - but I also know a hell of a lot of people."

He doesn't seem fazed by the wealth; and I start to feel quite tacky bringing it up. I ask what it's like to work with such people: people who have a reputation for being some of the most demanding characters in the world.

"Every single big name you know, I act for all of them. Every single one of the big Russian and Ukrainian Jews, every single one I know.

"It's very easy to deal with them. They are extremely easy, polite, pleasant and soft spoken."

But as well as being an influential figure in the super rich property sphere, Hersham was once known as a party boy.

Since he married his second wife, Olga, his social life has been curtailed.

"I don't go to any parties anymore. I used to like the London nightlife, but I don't anymore," he says. "What am I going to do as a married man in a nightclub?

"I have stopped because I work very hard and like traveling more than I like going to nightclubs. I prefer to go to kosher restaurants."

Even in his party days he kept Shabbat. "I have never been out on a Friday night and I have never had any such temptation to break Shabbat in my entire life. It never occurred to me. What's wrong with Saturday night?

He proudly declares himself FFB. I'm lost. "Frum From Birth," he sighs. "We have always been brought up in our family, from the day we were able to crawl, to know that we were religious. I knew I was going to yeshiva when I was eight years old."

He went to Menorah Primary School and Hasmonean High School before spending two years at the Kol Torah Yeshiva in Jerusalem. Today he's a regular at the Central Square Minyan in Hampstead Garden Suburb or Beit Baruch in Belgravia and regularly hosts his children and two grandchildren for Shabbat in the Hampstead Garden Suburb house, so they can benefit from the eruv.

On the day we meet, he is dressed in a crisp white shirt and royal blue jacket. Beneath his shirt, he's wearing tzitzit - he unbuttons his shirt to show me - and in his jacket pocket, he has a kippah at the ready.

He's sad that young people seem less religious nowadays.

"Quite a lot of kids I know who come from frum backgrounds allow themselves to break Shabbat and go out on Friday night," he explains. "Often the parents find it very difficult to restrict them."

I suggest it is hard to be very strict: kosher food or wine might not appeal. But he dismisses the suggestion, pointing to his two favourite kosher wines: Rosé du Castel (£26 a bottle) or the Blanc du Castel (£35). "Superb!"

He loves to eat in Golders Green's Met Su Yan and points out: "I think you have to remember where you are from, and what the precepts of your religion are and why they are set in stone.

"It's for your future and for the future of your generations

"When people remember that, they know it's not such a hardship not to go out to a restaurant. It's not such a hardship to be with your family at home. Then, they will bring their children and their grandchildren up that way."

He starts glancing at his watch.

I ask how he would like to be remembered.

"As a very good estate agent, selling some of the most exclusive properties worldwide to the super rich. As I get older, I realise that the only thing I am really good at is property."

He started out working in his father's successful company. Property was the smallest part, but became the most profitable.

"I can assure you that between the ages of 20 and 30 as a young man in the seventies, particularly from a semitic background, one did not control one's destiny, one was very much controlled by one's family. I went to school, I went to yeshiva, I read an undergraduate degree at Imperial College in Zoology, Biochemistry and applied Etymology; though my father told me I certainly wasn't educated well enough and I ought to do a degree in the law or accountancy.

"The reason I fell into estate agency, is simply because my father had put me in one of his businesses, and he was somewhat of a tyrant.

"I never thought of myself as being his heir to his business."

So, when he was 27 he struck out on his own. "My friend invited me to join him in a non-existent estate agency." One year in, he owned Beauchamp Estates.

He adds: "Every young man who works for an entrepreneurial father who made money from zero to hero always wants to prove himself.

"If you look at my children, and my cousins' children and all my friends' children - every single one of them from those sort of backgrounds are running their own business or being entrepreneurial. So I think it's in the blood, to tell you the truth."

With that, we sprint off upstairs. He shows me his new business cards (they are branded in his favourite colour, royal blue), puts a royal blue Beauchamp Estates brolly in my hand (also royal blue), and with that, I'm off.