Top silk Stuart Isaacs QC is leaving 4-5 Gray's Inn Square following the failed merger with Monckton Chambers.
Two juniors at the chambers are also leaving but the set has tempted in a senior junior from Fountain Court.
Leading commercial and European silk Isaacs is quitting after 22 years to join 3-4 South Square on 1 September.
Juniors Martin Chamberlain and Karen Steyn are leaving 4-5 Gray's Inn to join Brick Court Chambers and 11 King's Bench Walk respectively.
Isaacs says: "I received a number of invitations to join leading commercial chambers and of those I thought 3-4 South Square was ideal to continue my practice in commercial and European law for domestic and overseas clients. The set has expanded from its core practice area of insolvency and overlapped with my own interests."
Isaacs is rated among the top silks in the country for banking law as well as being a leading arbitrator. He is a member of the New York bar and was made a recorder in 1997.
He describes his move to 3-4 South Square as a great opportunity to join a forward-looking set, but declines to comment on the reasons for his departure. He does say, however, that leaving 4-5 Gray's Inn was not an easy decision.
Sources close to 4-5 Gray's Inn believe that Isaacs' decision was prompted by the possibility of it becoming a planning and local government set because of general unrest among the public law barristers. One source says: "It is not clear how many people are staying or going but we will know more by the end of the month."
Shanks says: "My reasons for leaving Fountain Court are entirely personal and totally amicable. I left because I was interested in pursuing more court-based work in the areas of public and employment."
Commenting on the departures, Shanks says: "Of course, the departures are not ideal but it is a career opportunity in terms of clients."