The index, based on the cumulative dollar net worth of all households in each country, is also forecast to show a big rise in the number of millionaire households.

Last year, seven countries - Canada, France, Germany, Italy, Japan, the US and Britain - had more than one million households worth more than $1 million.

During the next decade they will be joined by five more - Spain, the Netherlands, Australia, Taiwan and South Korea.

"Many new millionaires (will be) created in China, India, Russia and other countries that are undergoing rapid development," Barclays Wealth said.

"This trend suggests that a point will soon come when it is more appropriate to say that these countries are central players in the global economy, and should no longer be classed as emerging or developing," it added.