O'Neill hits back at those who have said that the BRICS is losing its shine.

To focus merely on a slowdown in the combined growth of the economies is missing the point, said O'Neill.

China's economy continued its steady expansion in the first half of this year with its GDP up 6.9 percent year-on-year to about 38.2 trillion yuan (5.6 trillion dollars), according to the country's National Bureau of Statistics.

Russia and Brazil suffered recessions in recent years, but Brazil's economy grew again in the first quarter of this year after a protracted recession and Russia achieved a growth rate of 2.5 percent year-on-year in the second quarter.

"The fact they have slowed down is an irrelevance if they are still way bigger than I thought 16 years ago - primarily because of China but also because of India, and not withstanding the problems that Brazil and Russia have had."

"So these people that say it is not so important because they have grown less, it is ridiculous," he said.

What's more, O'Neill has his eyes set on other nations that could also surprise the world in the coming decades.

"I would say going to 50 years in the future, there are probably four countries with potential to be as big as Russia or Brazil," said O'Neill.

"Definitely Indonesia, possibly Mexico, possibly Turkey and, excitingly, possibly Nigeria. But let us see - just because they have the potential it does not mean it will happen."

"The BRICS countries have already said they are open to other members. But I would not do that any time soon until we see clear evidence of any of those four becoming a lot bigger," he said.