Quinn Emanuel Urquhart & Sullivan’s London office has spent more than a decade 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 could now stand at as many as 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. Another person added, however, that so far only six associates have officially resigned.