Many of the world's largest economies may be weathering the toughest recessionary storms in living memory, but for those at the top there has rarely been an easier time to join the billionaires' club.

Some 210 multi-millionaires were propelled into the premier league of extreme wealth in the last 12 months as they achieved 10-figure fortunes and the world now plays host to a record 1,426 dollar billionaires, according to Forbes magazine's study.

This super-rich set together sit on wealth estimated at $5.4tn (£3.6tn) – equal to more than a third of the annual output of the US, the world's largest economy. Last year the billionaires' club held a combined wealth of $4.6tn.

At the top of the billionaire tree, once again, is the Mexican telecoms magnate Carlos Slim, with an estimated worth of $73bn, followed by the Microsoft founder Bill Gates, who has a fortune of $67bn. The success of the company behind Zara, the world's biggest rag‑trade operation, saw the retired Spanish entrepreneur Amancio Ortega – who still owns 60% of the business – climb into third place in the rankings. His fortune is put at $57bn.

Despite Spain being locked in one of Europe's most crippling recessions, with 55% youth unemployment, Ortega was estimated to have seen the biggest rise in wealth of any billionaire, adding $19.5bn to his pot. As a result, he has leapfrogged Warren Buffett, the investment tycoon known as the Sage of Omaha, who last month swallowed up the Heinz food empire for $28bn.

Buffett's wealth is put at $55.5bn. It is the first time in 13 years that he has not featured in Forbes' top three. Despite this slip, the rankings at the very top echelons of the billionaires' club remained remarkably static, dominated by wise heads that have weathered many recessions in the past. Of Forbes' top 10, eight are aged 70 or older.

Trade union leaders, economists and anti-poverty campaigners said the swelling fortunes of the fast-expanding billlionaire set signalled that levels of wealth inequality were fast approaching crisis levels.

The TUC general secretary, Frances O'Grady, said: "These latest findings from Forbes make for very disturbing reading. Trickle-down economists may love having a growing super-elite, but seem to forget the fact that rising pay inequality was a major cause of the financial crash.

"Faced with flat wages, many people borrowed to maintain their living standards whilst the very wealthy put their cash into ever more risky investments to squeeze out returns. Unless wealth is spread more broadly, we will be unable to build a sustainable recovery, as consumer spending will continue to flat-line."

Other senior figures to raise concerns over spiralling inequality include Angel Gurría, OECD secretary general, who said "widening disparities weaken the structures that hold our society together", while Christine Lagarde, head of the International Monetary Fund, recently warned business leaders in Davos that "the economics profession and the policy community have downplayed inequality for too long."

Among the young turks to join the billionaires club in recent years are the Facebook founder Mark Zuckerberg, 28, and his former collaborators Eduardo Saverin, 30, and Dustin Moskovitz, 28. Despite a fortune estimated at $3.8bn, Moskovitz is said to bike to work, shun business class flights and, according to Forbes, "pitches his own tent at [Nevada desert counter-culture festival] Burning Man". The Twitter co-founder and punk music fan Jack Dorsey also scrapes on to the list, with a fortune put at $1.1bn.

Women were well represented among newcomers to the Forbes list, though they still only account for 138 of the world's billionaires, albeit up from 104 last year. The world's richest woman is the 90-year-old French cosmetics heiress Liliane Bettencourt, who is the ninth-richest person internationally. Her L'Oréal empire is best known for its "because I'm worth it" television advertising slogan.

The US is home to 442 billionaires, according to Forbes, with 366 in Europe, 129 elsewhere in the Americas and 103 in the Middle East and Africa.

Despite turbulent times for many of the largest economies in the world, 210 new billionaires were minted in the last 12 months – three times the number of individuals who fell off the list. This concentration of wealth took place despite a strengthening in the dollar against many major currencies.

Credit Suisse, a Swiss bank that specialises in catering to super-rich clients, estimated last autumn that the world's richest 1% – that is, those with wealth of $710,000 and greater – control 46% of global assets. In its annual Global Wealth report, the bank estimated that the number of individuals with fortunes in excess of $50m around the world had reached 84,500. "Notwithstanding the credit crisis and the more recent setbacks, the past decade has been especially conducive to the establishment of large fortunes," Credit Suisse concludes.

The tax campaigner James Henry, a former economist with the global consultancy firm McKinsey, has estimated that between $21tn and $32tn of the world's wealth had been stashed, tax-free, in offshore investments – with about half of this sum controlled by the world's richest 91,000 people. "Almost all of it has managed to avoid all income and estate taxes, either by the countries where it has been invested and or where it comes from," his study found.

The highest-ranking British billionaire on Forbes' list is the Duke of Westminster, Gerald Grosvenor. His Grosvenor Group owns large tracts of land in Mayfair and Belgravia and can trace its roots back to 1677, is worth $11.4bn. Fourth on the UK rankings was his fellow land-owning aristocrat Lord Cadogan, whose Cadogan Estates includes a lot of real estate in Chelsea.

Foreign billionaires who have made London their home and who feature in many UK rich lists were not classed as British by Forbes. Those not qualifying as British billionaires included the steel magnate Lakshmi Mittal, the Russian mining and investment tycoon Alisher Usmanov and the Chelsea football club owner Roman Abramovich.