UBS Warburg is advising Vodafone on its fourth deal in nine months with Japan Telecom, making the UK's largest mobile phone group the largest foreign corporate owner of a Japanese company.

Vodafone has launched an offer for 21.7% of Japan Telecom, with the recommendation of the Japan Telecom board, which could see Vodafone increase its stake in Japan's third largest fixed line operator from 45% to 66.7%.