Since the start of the year, the invincible aura surrounding the world's biggest emerging economies - Brazil, Russia, India and China - has evaporated as the combined value of their stocks has tumbled by about 65 per cent.

The collapse in these markets, which had risen dramatically since they were first grouped together as the Brics in 2001 by Goldman Sachs, has raised serious questions about the worth of combining them for an investment portfolio.