The Children's Investment Fund, the London hedge fund, lost more than $1bn in its worst month ever in June as activists were hit particularly badly by the poor markets.

TCI, which manages more than $10bn and made its name taking on Deutsche Börse and ABN Amro, slumped 12½ per cent in the month, according to investors in the fund, to leave it in the red for the first half of the year. The fall topped the five-year-old fund's previous biggest drop of May 2006, when a sudden market shift hurt many funds.