High-frequency trading firms contributed to a surge in activity in May that took the European equity market over €1 trillion ($1.24 trillion) for the first time in a single month since October 2008, immediately after the Lehman Brothers collapse.

The value of shares traded in May crept above the €1 trillion mark on Thursday last week, beating the previous highs since Lehman of €849bn in April this year and €810bn in October 2009, according to Thomson Reuters.