Yes, the SIS is subject to the Public Records Act

I understand there's some stuff going round about how the SIS "was removed from the list of public offices covered by the Public Records Act in 2017". The context of course being their records derived from US torture, which will be disposed of or sealed.

The good news is that its wrong. Yes, a clause in consequential amendments schedule of the Intelligence and Security Act 2017 repealed the explicit reference to the SIS from the list of public offices in the Public Records Act 2005. But that was because another clause in the Act itself added it to schedule 1 of the State sector Act 1988, making it a department of the Public Service. Which of course are the very first thing in the list of types of bodies that are public offices covered by the Public Records Act. So, they're covered. It might be next-to-impossible to ever see anything they have ever held, but at least it will be kept so historians in a hundred years can look it.