Ikea founder overtakes Bill Gates in the wealth stakes. (And he assembled it all himself)

He describes his only luxury in life, a small Provençal vineyard, as a "very expensive hobby". His car is an 11-year-old Volvo, he trawls the internet for flight bargains and always travels in the economy cabin. For a man of average wealth, such behaviour would be considered prudent. But according to financial experts in his native Sweden yesterday, the figure behind such careful spending habits now also happens to be the richest individual on the planet.

Ingvar Kamprad, the founder of Ikea ­ and as such, responsible for a global epidemic of head-scratching over self-assembly wardrobe instructions ­ has overtaken Bill Gates, the Microsoft billionaire, as the wealthiest human being by amassing a personal fortune of $58bn (£32bn).

The figure, which was hotly contested by Ikea, highlights the remarkable success of the publicity-shy entrepreneur, who turned flat-pack bookshelves into a vastly successful business despite a battle with alcoholism and damaging publicity arising from a youthful flirtation with Nazism.

Research commissioned by a Swedish business magazine, Veckans Affarer, claims that previous assessments of Mr Kamprad's wealth, which put his fortune at $13bn (£7.2bn), were gross underestimates.

The new assessment claims that the furniture magnate, who no longer has a role in the daily running of Ikea, is still the ultimate owner of the private company, which is split into multiple subsidiaries and is headed by a charitable foundation based in the Netherlands.

As a result, the famously parsimonious Mr Kamprad is propelled from the relative obscurity of 13th place on the latest version of the Forbes magazine rich list, regarded as the gold standard for ranking vast wealth, to the holder of the biggest pile of individual lucre in the world. The estimate puts Mr Kamprad, 77, ahead of Mr Gates, who said to be worth £26.9bn, and the American investment guru Warren Buffet with £20.2bn. Only the Walton family, which owns American retail monolith Wal-Mart, is worth more, with an estimated joint fortune of £54.6bn.

Bo Petterssen, the financial analyst and journalist who researched Mr Kamprad's wealth for Veckans Affarer, said: "Because it is a private company, it has been notoriously difficult to find out the true value of Ikea and also Mr Kamprad's wealth. "But we have looked at private figures from Dutch archives which allow us to assess the profits and what Ikea would be worth if it was floated on the stock market.

"Because we argue that Mr Kamprad is still in control of virtually 100 per cent of the group, we can estimate his personal fortune. It is a large one."

Since its foundation by Mr Kamprad at the age of 17 as a door-to-door supplier of nylon stockings and wallets, Ikea has made its founder's non-conformism a trademark, whether by under-cutting its early competitors by collecting stock from suppliers under cover of darkness or recently urging its dowdy British customers to "Chuck out the chintz" in an advertising campaign.

Ikea was less than happy to accept the reassessment of Mr Kamprad's wealth. The company insisted that the decision by Mr Kamprad in 1982 to put Ikea under the control of the Stichting INGKA Foundation, a charitable trust that supports various architecture and design institutions, meant his personal wealth was not connected to Ikea.

Marianne Barner, a company spokeswoman, said a figure of £32bn based on a stock market valuation of Ikea was therefore seriously misleading.

She said: "This is completely wrong. It's a mistake that is made all the time. Estimating the value of the company, including all the stores, and saying it's all Ingvar's, that is totally wrong. Ingvar Kamprad does not own Ikea."

But the company declined to offer an alternative figure for Mr Kamprad's personal wealth or a breakdown of the destination of the profits from its annual sales, which last year reached $12.2 bn (£7.1bn) and have increased by an average of 15 per cent per annum in recent years.

A City analyst said: "It is a private company with a very specific structure. It doesn't have to answer to shareholders so it can pursue a long-term social agenda. But it also means that it doesn't have to discuss how much its founder is really worth."

Whatever the true extent of Mr Kamprad's fortune, there can be little doubt of the business genius and eccentricity that made it possible. Brought up on a farm in southern Sweden, his father initially despaired of the son who had to be constantly coerced into milking the family's dairy herd.

But by the age of 20, Mr Kamprad had expanded his retail company ­ named after his initials and the first letters of his parents' farm and the village where they lived ­ into furniture and produced a mail-order catalogue that distributed its first flat-pack kits using the local milk van.

His first store opened in 1953, and when it became too busy for staff to man both the showroom and the tills, Mr Kamprad invented the retail system that helped propel Ikea to phenomenal success: the customers were left to pick up their home-furnishing bargain from the warehouse and the "co-workers" took the money.

Ikea now has 174 of its blue and yellow warehouse stores in 36 countries. The expansion of the group, which also owns Habitat in the UK and has its busiest store worldwide at Brent Park in north London, has succeeded despite Mr Kamprad's self-confessed early brush with alcoholism and the revelation in 1995 that he had attended meetings of a Swedish pro-Nazi party between 1945 and 1948.

Mr Kamprad said: "This is part of my life I bitterly regret. At first I got in touch with a pair of Nazified organisations and perhaps I even became a member, I have forgotten. However, after a couple of meetings in pure Nazi style, I quit."

The entrepreneur, whose first Ikea slogan was "Not for the rich but for the wise", now lives in Lausanne, Switzerland. As well as eschewing first-class travel and restricting his foreign property portfolio to his French vineyard, he also waits until the afternoon to do his fruit and vegetable shopping at the local market because that is when traders drop their prices. In one of his rare interviews, he said: "If I start to acquire luxurious things then this will incite others to follow suit. It is important that leaders set an example."

Mr Kamprad's wealth appears to have caused no resentment in his native land. Mr Petterssen said: "He is seen as a little eccentric but he is also a hero. After all, he is spreading Sweden's colours across the world."