Regulators have anxiously watched assets in exchange traded funds swell to record levels following the financial crisis, but they have so far uncovered little support for theories that the products could be responsible for the next market crash.

Globally, the ETF industry is now responsible for some $5.1tn in assets — up from $774bn at the end of 2008. That explosive growth caught the attention of financial watchdogs, as critics of the vehicles alleged that a mismatch between ETFs and their underlying assets could lead to havoc if  investors were to try to sell all at once during a severe market downturn.