The informant who helped U.S. tax authorities build their ground-breaking case against UBS AG is asking a Florida federal judge to postpone his prison term and reconsider his 40-month jail sentence.

Former UBS private banker Bradley Birkenfeld, who is scheduled to report to jail by Jan. 8, made the requests in a court motion Saturday night and said he is "ready, willing and able" to assist the government in prosecuting additional U.S. clients of UBS.