Clayton Utz' Chief Executive Partner David Fagan said while he was disappointed at the departures, the firm was in great shape and would continue to deliver the exceptional service clients had come to expect.

"Partner movements such as this occur in the lifecycle of a firm. Clayton Utz is in excellent shape and continues to be one of the strongest performing firms in the market," he said.

Clayton Utz is a national Australian firm, one of a handful with such a spread. It concentrates on corporate matters. Headquartered in Sydney, the firm boasts an impressive client list.

Allen & Overy is huge: it has more than 5,000 people around the world. But although it has a long history in Asia Pacific, it has not had a formal presence in Australia. It recently announced that it would open an office in Sydney but gave little information as to its plans.