Freshfields in Japan has unveiled plans to become a top-five Tokyo firm within the next five years.
The Tokyo office has already trebled in size to 12 lawyers practising Japanese and international law, since last May, when it became the first UK firm to form an association with a Japanese firm, run by senior bengoshi, Naoki Kimani.
Charles Stephens, Freshfields' managing partner in Tokyo, said the the association's success would open the floodgates for other City firms to set up large practices in Tokyo offering international and local law.
Stephens said his office hoped to have 20 lawyers in place by the end of this year and aimed to employ as many as 50 in five years time.
Freshfields is the only UK firm with a Japanese affiliate, although Sullivan & Cromwell, White & Case, Baker & McKenzie and Gide Loyrette Nouel have local associations.
Japanese law forbids bengoshi from joining foreign firms as employees or partners. Jonathan Imman, Linklaters Tokyo partner, described the status of the relationship with bengoshi as "uncertain".
Imman heads up the legal services committee of the European Business Community group in Tokyo. He said he would be meeting a delegate from the European Commission to keep the liberalisation of Japan's legal system on the agenda.
Imman said his firm also had plans to grow in Japan, "to about 16 or 17 lawyers this year".