The top London firms have responded to the threat posed by the expansion of their US rivals into Europe by expanding their US law practices by more than 20% during the past 12 months, according to a survey by Legal Week Global.

At the start of May, London-based firms together employed 1,238 US-qualified lawyers, which rises to more than 1,300 if Clifford Chance’s (CC) recent raid on Brobeck Phleger & Harrison is included.