Everything in life happens for a reason,” says David Khalili. “Warren Buffet says the reason we are sitting in the shade is because someone put a seed in the ground.” And the reason I am sipping Lafite ’85 is because Khalili, like Buffet, is very rich.

How rich is a matter of some dispute. When he was in The Sunday Times Rich List in 2007, his worth was put at £5.8 billion on the basis of his 25,000-piece art collection. But, he says, the figure is meaningless.

“Our five collections are irreplaceable,” he e-mails, “priceless and inestimable, regardless of the amount of time or money available. Any published figures, in The Sunday Times Rich List or elsewhere, are therefore purely speculative.”

The collection won’t, he says, be sold, and it can’t be valued because there is nothing with which to compare it. It’s like Everest or the Great Wall of China — just, sort of, there.

But exact sums aside, rich is rich, and Khalili is damned rich. A vulgar sentiment, I know, but one that’s hard to avoid when you are sipping Lafite amid tens of thousands of square feet of prime Old Burlington Street freehold and dazzling art. Outside are his chauffeur and his car, a Maybach 62 (£300,000). These are his offices, the headquarters of his foundations and a gallery of some choice pieces to show to the great and the good — or, in this instance, me. Tony Blair had just been in to discuss interfaith activities. There’s a display case of enamels — Fabergé eggs and other such knick-knacks.

Also, he’s controversial — but I’ll come to that.

He shows me round the gallery. First there’s a piece of marble, quite small. It rests casually against a wall. This particular knick-knack is a good starting point if you want to know who this man is.

“In 1972 I was driving for 16Å hours from New York to Miami and back. I’d go there to buy stuff, put it in my car and take it back to New York. I used to stop and visit different antique shops.

I walked into one garage sale and saw this. It’s 550BC, one of the earliest Greek friezes you will ever see. It’s the Mona Lisa of all friezes, earlier than the Elgin Marbles. I bought it for $120.”

It’s the Khalili story in a nutshell — the ultimate Antiques Roadshow. He just, he says, sees stuff.

If there was an Olympic event called “Eye for a Bargain”, he’d be our brightest medal prospect. Of the five collections, Islamic art (AD700-1900) is the biggest, then there’s Japanese works from the Meji period (1868-1912), Swedish textiles (1700-1900), enamels (1700-2000) and Spanish damascened metalwork (1850-1900). He picked a previously neglected sector and bought everything he could lay his hands on. And — but you have probably guessed this already — he started from nothing.

First, let me try to conjure this extraordinary man. A 63-year-old Iranian Jew with dual British-American nationality, he talks like a Geordie — really. It is the “i”, which always come out as “oi”, so “I decided” becomes “Oi decoided”. He seems startled when I point this out and denies he ever says “I” at all, always “we”. But then he gets it.

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