Opposition" for the outspoken views he presented in Parliament.
He was the official Leader of the Opposition in Parliament from 1964 to 1969.
Although he was originally a leader of the Labour Party of Malaya and the Socialist Front coalition which Labour had joined, Tan later co-founded Parti Gerakan Rakyat Malaysia (Gerakan), and also Parti Keadilan Masyarakat Malaysia (Pekemas) after he became disillusioned with Gerakan.