This week the world’s most expensive painting Nude, Green Leaves and Bust goes on show at Tate Modern on London’s South Bank.

It was bought at auction in New York last May when it sold at Christie’s for $106.5m (�66m). It was bought by a mystery buyer who, according to press speculation, is believed to be Chelsea FC boss Roman Abramovich. The fact that it has been offered to Tate Modern, it seems to support the theory that the painting went to a UK buyer.

But, the identity of the purchaser to me seems the least interesting aspect of this story. For me the real question is why is Picasso’s Nude, Green Leaves and Bust worth �66 million? And if it is – it is certainly a magnificent work – then why aren’t a whole host of other equally inspired paintings worth the same?

Is it just the fact that there is a famous name attached to the painting that makes it worth the sum?

This is the commercial reality I’m afraid. As much as the na�ve purist in me rails against such a thought, equally inspired works by less well-known names will never attract the same prices. The quality of the work has nothing to do with it. In fact art rarely has much to do with it. It is the collectability factor which puts the zeros on the price tag.

This is the world of art bought as an investment. This is a world where people not interested in art, as such, use advisors to buy work which they believe will increase in value.

The owners may never see the painting. It can be squirreled away in a secure vault or loaned out to a museum and the owner may never see it. It begs the question why did you buy it then?

This seems to have been the fate of Nude, Green Leaves and Bust before the recent sale.

The last time the painting came up for sale was in 1951, when it sold for $19,800 to Los Angeles-based collectors Sidney and Frances Brody. During that time they hardly let it out of their sight and it was exhibited in public only once – in 1961, to mark the artist’s 80th birthday.

Nude, Green Leaves and Bust was a reflection of Picasso’s lusty pursuit of women. It was inspired by a young muse Marie-Th�r�se Walter. It was a passionate painting, completed in a single day in 1932.

At the time Picasso was a middle-aged man and was in the middle of a torrid affair with Walter. She was a young woman whom Picasso first encountered in 1927 when she was 17. He spotted her leaving a Paris Metro station and accosted her.

Walter later told the story of how he took her by the arm and said: “I am Picasso! You and I are going to do great things together.”

Their passionate affair lasted until 1935 when Picasso took on a new mistress – Dora Maar.

Such stories are part of a painting’s life, part of its allure and mystery.

This sense of passion, this sense of drama, this obsession is captured on canvas. It should stir your own imagination. It can’t do that if it is locked away unseen.

People should buy art because they like what they see. Anyone going into an art gallery and saying to the owner: “Is this a good investment?” or “How much will this be worth in ten years time?” should be shown the door. Sadly, commercial realities mean this would never happen.

Instead, the gallery should pose his own questions: “Do you like it?” or “Are you going to hang it in a place where you are going to see it?”

The good news about the Picasso is that its new owner has had the good sense to offer it to The Tate where it will form the centre-piece of the gallery’s new Pablo Picasso room. The big names of art have always attracted attention but fame can be a double-edged sword. Fads and fashions change and the prices that the work can command reflect those changes.

Should the purchase of art come with a warning similar to that given when buying shares. “The value of this purchase can go down as well as up.”

It has always annoyed me that people like Charles Saatchi have been lauded for having a knack of discovering young artists before they become famous.

Time and again you read that Saatchi picked up early work by an artist, people like Damien Hirst, Gavin Turk and Sarah Lucas, at Royal College of Art graduation shows and suddenly the value of their work goes through the roof. The unspoken part of this admiring genuflecting is: “How does he do it?” and “Why can’t I?”

The reasons are fairly simple. Charles Saatchi genuinely loves art.

He spends a lot of time and money pursuing his passion, which is why he goes to graduation shows.

Saatchi is well respected in art circles, so any artist he champions will automatically gain attention and this translates into higher gallery prices, which makes more collectible which again pushes up the price. It’s a self-fulfilling prophesy.

The people who wish they could spot artists like Saatchi are the investors who want to pay �20 for a work by a young artist and then sell it, a decade later for �20 million. Their interest in the artist and his work rarely extends beyond the money it generates for their bank account.

It’s a pity that it takes people like Charles Saatchi to legitimise artists.

Also serious art is very London-centric and I resent the implication that nothing innovative and exciting happens in the regions.

There are plenty of terrific artists in East Anglia, pursing their own vision and turning brilliant work and yet the prices they can command are a tiny percentage of their feted-London contemporaries. This difference in price is nothing to do with the quality of their work. It is all about their visibility and their collectability.

Had Maggi Hambling immediately returned to East Anglia having graduated from Slade and set-up a studio in north Suffolk, I suspect her work would be little different from what she is doing today but her profile would be greatly reduced and her price-tag would be fraction of what she can now command. It’s all about having that London-credibility.

Art has to have a relatively high price because you are paying not only for not only the man hours involved in creating a handmade work but also for the uniqueness of the work.

It’s a hand-crafted one-off. And you also have to pay for the years of experience which has gone into this wonderful finished object – be it painting, sculpture or multi-media.

Art prices need to be higher than for mass-produced objects but they shouldn’t be beyond the reach of the ordinary art enthusiast willing to make an investment.

There has to be a sensible middle ground.

Good art should never cost more than your car, let alone the house you live in.