Not just a right, with independence they have to take over their own self defence and can't just leave it to the British. Perhaps offer the British basing rights as part of a mutual defence treaty? IIRC there were at least some in government that realised that Hong Kong wasn't going to be around forever and that Singapore might be limited by size and future politics. Or since as Xhavnak mentioned they were concerned about maintaining 'British interests' arrange it as part of independence deal, something like the the Sovereign Base Areas on Cyprus might be a bit much but a very long term lease for an army/air force base somewhere out of the way and port facilities for ships might be achievable.War?!! Well, better establish Sarawak Armed Forces ASAP. Things gonna get ugly... Especially from the hands of Sukarno... Can't imagine watching the sight of General Kanang Anak Langkau...
Besides, as a Dominion, Sarawak have a right to establish their own armed forces...
As you're a local random question I wanted to ask, but is there anything special or important about the land between the two areas of Brunei? Always seemed slightly odd the place being split in two with Temburong being just off to the east. When mulling over what to do with Sarawak in some other timelines I was considering, generally just ended up giving north-western Limbang Division the bit separating Brunei back to help smooth relations with them.