As UK and Malaya began the process of implementing their Grand Design" to transfer the Borneo territories to Malaya, 3 former British colonial territories exercised their right to decide on self-determination.
1. In 1961 the British Cameroons, Africa the people were allowed the right to choose between merging their country with Nigeria or the Southern Cameroons. But they did not have a choice to choose independence and this issue has now being revived in the Cameroons.
2. In the West Indies Jamaicans voted to leave the Federation of the West Indies AND the Federation was dissolved. A referendum on continued membership of the Federation of the West Indies was held in Jamaica on 19 September 1961. Voters were asked "Should Jamaica remain in the Federation of the West Indies?" The result was 54.1% voting "no", resulting in the country leaving the federation and its dissolution in 1962. Voter turnout was 61.5%.
3. In Dec. 1962 Britain also acknowledges Nyasaland’s right to secede from Central African Federation.
On 1 Sept 1962 Singapore proceeded to hold a referendum on merger with "Malaysia". There was no option for the people to reject "Malaysia". And in 1965 Singapore freely exited "Malaysia".
However, the British & Malayan governments totally blocked any demands for a referendum on the issue in Sabah and Sarawak.
The exit option was also denied to the Sabah and Sarawak people despite what Lord Lansdowne the IGC Chairman said when Sarawakians demanded an "exit clause" in the Malaysia Agreement 1963.
He said “any State voluntarily entering a federation had an intrinsic right to secede at will”. He obviously had in mind the above examples of African and Caribbean examples of countries exiting as members of a federation.
While S'pore freely exited Malaysia by 1965 Sabah and Sarawak were blocked by Malaya from doing so..
Source: Borneo Wiki