Quinn Emanuel Urquhart & Sullivan’s London office has spent more than a decade rapidly building its highly profitable team of star litigators. But on Tuesday, it saw three top partners leaving at once to join Willkie Farr & Gallagher.

In addition, the number of associates joining the walk-out now stands at 12—making it a total of 15 lawyers—according to a person with knowledge of the hires, meaning it is one of the biggest U.K. team moves of the year.