Many of the world’s regions have switched places in the UBS rankings as currencies fluctuated in the wake of the financial crisis.

UBS Bank used to rank London the most expensive city in the world – but it has now plummeted to the 22nd spot. All in just one year.

In the 2009 list, Oslo has been crowned the most expensive city in the world, followed by Zurich and Copenhagen.

Tokyo is the world’s most expensive city, according to Mercer’s 2009 Worldwide Cost of Living survey released today, with the cost of living up 13.1% from 2008.

Japan’s capital is followed by Osaka and Moscow, which held the top spot in last year’s rankings. Geneva comes in fourth.

The significant changes from last year are due to massive swings in exchange rates, with many currencies at their weakest in years against the U.S. dollar, during the March 2009 survey period.

Mercer has just released its top 50 most expensive cities in the world based on cost of living.

Mercer’s Worldwide Cost of Living Survey 2008 is used to help multinational companies and governments determine living costs for their expatriate employees, who usually demand a relatively high quality of life.

Mercer’s survey covers 253 cities across six continents and measured the relative cost of over 200 items in each place, including housing, transport, food, clothing, household goods and entertainment.