Lee won the Tanjong Pagar seat in the 1955 elections. He became the opposition leader against David Saul Marshall's Labour Front-led coalition government. He was also one of PAP's representatives to the two constitutional discussions held in London over the future status of Singapore, the first led by Marshall and the second by Lim Yew Hock, Marshall's hardline successor. It was during this period that Lee had to contend with rivals from both within and outside the PAP.[10]
Lee's position in the PAP was seriously under threat in 1957 when pro-communists took over the leadership posts, following a party conference which the party's left wing had stacked with fake members.[27] Fortunately for Lee and the party's moderate faction, Lim Yew Hock ordered a mass arrest of the pro-communists and Lee was reinstated as secretary-general. After the communist 'scare', Lee subsequently received a new, stronger mandate from his Tanjong Pagar constituents in a by-election in 1957.