 Faced with the prospect of a takeover by the pro @-@ communists , UMNO changed their minds about the merger . On 27 May , Malaya 's Prime Minister , Tunku Abdul Rahman , mooted the idea of a Federation of Malaysia , comprising existing Federation of Malaya , Singapore , Brunei and the British Borneo territories of North Borneo and Sarawak . The UMNO leaders believed that the additional Malay population in the Borneo territories would offset Singapore 's Chinese population . The British government , for its part , believed that the merger would prevent Singapore from becoming a haven for communism . 
