Intellectual property partner Stephen Jones has left Allen & Overy (A&O) for competitor Baker & McKenzie (B&M), to head up its patent practice group and trademark's unit.
It is the first partner A&O has lost in London in the last 12 months. Jones joined A&O in 1995 and was made a partner in 1997.
A spokesman for the firm said although it was sad to lose any partner, Jones was the most recently promoted of the six-partner, 25-lawyer department.
Catriona Smith, head of IP at A&O, said although work was "thriving" the department was managing without Jones.
She added that the department was planning to recruit in the near future, but not necessarily to replace Jones.
Jones will join partner Michael Hart at B&M, a colleague from his time at Linklaters where he worked for 10 years. Jones has also previously worked at Boodle Hatfield and ICI.
Hart said that B&M's department had better synergies with the type of work that Jones specialised in and that this was the reason for the move.
One lawyer from a competing firm said that this was the likely reason for his departure. He said that Jones was a trademark specialist and aspects of this law were stronger at B&M.
Hart said B&M's IP department was expecting to take on four other associate lawyers in the next four months, which would bring the total number of lawyers in the department to 21, including seven partners.
Russell Lewin, the managing partner of B&M's London office, said: "Stephen's very rare triple qualification as a solicitor, patent attorney and trademark attorney will enhance our already strong IP practice."
Jones, who is scheduled to start at B&M on 1 March, was abroad at the time of this issue going to press and was consequently unavailable to comment.