U.K. Parliamentary Papers on Proquest. This is a rich database which includes the House of Commons Parliamentary Papers from 1715 until the present. You will find detailed sources for Britain, its colonies and the wider world. There are many documents of interest to New Zealand historians for instance the Correspondence respecting Memorial by certain Maori Chiefs 1884.
This database is straight forward to use, with a simple search or advanced search function. The results are sorted by relevance but you can also sort by date. It's easy to create a personal profile which enables you to save your research.