I wanted to share a new collection with you all that will be of interest.
Archives New Zealand has recently acquired a set of Police Special Branch recording sheets for the years 1920-1945 (1945-57 is coming next year): http://www.archway.archives.govt.nz/ViewEntity.do?code=24890
This series contains records that were known as Old Police Records (OPRs) in the New Zealand Security Intelligence Service (NZSIS). The OPRs index the reports of the New Zealand Police Special Branch, which existed from 1920 to 1956, and consist of individual Special Branch Recording Sheets, each recording the receipt of a report and collected (mostly) into annual files.
The Recording Sheets contain things like name of individual, and a line on their movements (ie 'attended CP meeting 21/5/31' for example). The actual files and reports referred to in the sheets are held on separate classified files, which will be coming to Archives New Zealand next year.
Of what I have seen so far, they are amazingly detailed, although a number of personal files have been destroyed. For example, I've recently had copied full reports of the founding of the Communist party in 1921, including a speech by Andy Barras in which he is challenged by a wobbly about putting communists in Parliament!
Will update you all once the full set is there.