Sarawak & Brunei in Britain's colonial archive

The recently released imperial files in Britain are said to have entries on Sarawak as well as Brunei. What happened there and when ? Julian Thompson''s book The Imperial War Museum Book on Modern Warfare provides an account of an 'secret war' there from the perspective of a British military historian. 'How accurate and balanced is the account ? Are there other accounts that have not surfaced for various reasons ? Why did Brunei 'choose' not to join Malaysia like Sarawak (or Sabah) ? It is not immediately known whether there are ''stories'' on Singapore. Certainly, to render the many files intelligible, 'there is a need for an overall context for dots to be made lines '(and lines to form pictures). Seen in this light, 'Julian Thompson''s work is useful although readers may not share his interest and/or worldview when he wrote the book.