As any partner at newly ‘merged’ firm DLA Piper Rudnick Gray Cary Cuthbert Dibble & Grubb will tell you, transatlantic unions between law firms are notoriously tricky to get right.

Many and well-documented, the problems could be convincing one set of partners to water down their share of the loot, or persuading the other to cede 200 years of independence to a bunch of overbearing Yanks.