Three of the world's biggest investment companies secured more than two thirds of the net new money that flowed into exchange traded funds globally in 2017, as the booming sector passed the $4.5tn mark.

Data from the research firm ETFGI shows that 69.4% of the net $620bn allocated to ETFs in the year to December 20 went to funds managed by BlackRock, Vanguard and State Street. BlackRock's iShares division consolidated its position as the world's largest ETF business by taking 40% of the inflows.